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Research methodology
contents Introduction to research Definitions Research Thesis Dissertation Why to do a research Categories of research Research methods & research methodology Procedural steps in research Research strategy epidemiologic studies
Introduction
Investigation using scientific procedures, by searching again and again to find out the truth
Research is the continual search for truth using the scientific method. It is the pursuit of the truth with the help of study, investigation, observation, comparison and/or
definitions
Research (WHO Health research methodology, 1992, a guide for training in research methods):
Research is a quest for knowledge through diligent search or investigation or experimentation aimed at the discovery and interpretation of new knowledge. Scientific method is a systematic body of procedures and techniques applied in carrying out investigation or experimentation targeted at obtaining new knowledge. Here research and scientific methods may be considered a course of critical enquiry leading to discovery of facts or information which increases
Thesis
(according to Oxford English dictionary)
A proposition laid down as a theme to be discussed and proved. A discussion to maintain and prove a thesis especially written or delivered by a candidate for university degree- Ph.D
Dissertation:
Dissertation means “to discuss”. It is an academic activity laid down by the partial fulfillment of MDS
university for the
degree.
It is an exercise to train a PG student to plan, execute, evaluate, write and report a scientific project. It is an in-depth study of a particular topic which contributes new information and knowledge in the field A formal, often lengthy treatise (a book or writing of some particular subject, one containing a methodical discussion or exposition of principles of subject) or discourse, especially one
It is a pre-requisite or academic activity for acquiring a masters degree or doctorial.
To find out the truth which is hidden and which has not been discovered yet.
To contribute new knowledge to the existing one as the scientific knowledge develops in increments.
As a profession to conduct research in various aspects.
To solve an existing health problem.
Categories of research
1.
Empirical research and theoretical research Basic research and Applied research
Empirical
Observational research
Experimental research
Basic or pure research
It is usually considered to involve the search for knowledge without a defined goal of utility or specific purpose.
Eg. The microbiologist, whose expertise is the identification of pathogenic micro organisms may conduct research in-vitro, in a laboratory on bacterial reproduction, growth and endotoxin production without any direct application to clinical dentistry. Probably, the researcher is interested in monitoring endotoxins produced over the life cycle of bacteria to determine a pathogenecity.
Applied research
It is problem oriented and is directed towards a defined and purposeful end.
Eg. An oral health researcher investigating the relationship between periodontal disease and myocardial infarction may use the findings of the microbiologist as a theoretical framework to test the relationship between bacterial endotoxins, periodontal disease and myocardial infarction in animal and then in human subjects
Research methods
methods/ techniques that are used for conducting research are termed as research methods or research techniques.
1. 2.
3.
They fall into 3 groups 1. Those concerned with collection of data 2. Those statistical techniques which are used for establishing relationship between the data and the unknown
Research methodology
It is a way to systematically solve the research problem. It is necessary for the researcher to design his methodology for his problem, as the same may differ from problem to problem i.e. 1.
2. Why a research study has been undertaken 3. 4. How the research problem has been defined 5. 6. In what way and why the hypothesis has been formed
4. 5.
4. What data has been collected 5. What particular method has been adopted for collection of data 6. Why a particular technique of data collection has been used
And a host of similar questions are usually answered when we talk of research methodology, so that research results are capable of being evaluated either by the researcher himself or by others
Procedural steps in research
Selection of problem for investigation-further exploration Inexperienced-seek opinion –senior Constructing –essential starting point
Review literature Modern electronic research Abstract collection held on CD-ROMS-enables –key words Medline and psyclit database Role of systemic review grown recently-cochrane collaborationreviews from volunteer researchers internationally adds them to a bank,which is open for inspection by interesting parties.
Specifying study design
Selection of measures: many measure ,assessments Eg:self report rating scales for dental anxiety,observations,interviews,stand questionnaires
simple rating scale can be given a no.1-strongly agree 2-agree 3-undecided 4-disagree 5-strongly disgree May not exist for the study ,this may necessiate the development of new scale. should possess Reliability and validity
Selection of sample:
Sampling techniques-inorder to provide information ,can be generalised to cover the whole population.
Writing a protocol: aims & objectives,method,materials,sample ,procedure
Ethical approval Pilot work Main study Analysis of results Report writing publication
Research strategies Selection
of a research strategy is the core of a research design and is probably the single most Important decision the investigator has to make, i.e. whether to undertake a descriptive, an analytical or an experimental study.
Classification of Epidemiologic studies
Decscriptive study
Concerned with observing the distribution of disease or health related characteristics in human population Eg. Surveys. Defining population:denominator Defining the disease:operational definition. Describing disease-time,place and person Time: Short term fluctuation: 1. Common source epidemics-single,continuous 2. Propagated epidemics-person to person transmission of infectious agent---epidemics of hepatitis A and poliomyelitis
Periodic fluctuations: Seasonal –communicable diseases like measles,varicella,malaria Eg:upper Resp tract infections inc during winter and GI inf in summer Cyclic trends-measles-incidence every 2-3 yrs Influenza occurs at intervals of 7-10 yrs Long term fluctuation Changes occur over long period of time,change in frequency encompassing sev decades Eg:CHD,diabetes,lung cancer shows upward trend in 50 decades and TB, typhoid downward
Place distribution: Interanational National-endemic disease like goitre,flourosis Rural-urban-lung cancer,cardiovascular accidents-urban
Person distribution:age sex Measurement of disease :morbidity and mortality indicators
Expressed in terms of incidence and prevalence
Comparing with known indices:comparision b/n different population and subgroups of same populn-clue to etiology Formulation of hypothesis:relating to disease etiology specify-population,sp cause ,expected outcome,dose-response r/n,time-resp r/n. Eg:smoking of 30-40 cigarettes/day causes lung cancer in 10% of smokers after 20 yrs of exposure. Uses: 1. magnitude and type of disease in community 2. Clues to etiology 3. contributes to research
surveys
Surveys are methods of scientific or systematic collection of data, compiling, presenting in order (useful manner), analysing and evaluating them
The focus of attention must be on the following a) Formulating the objective of the study-obj describing what is to be measured,resources
b)
c) Designing the method of data collection eg. Questionnaires, interviewing, examination of records or observations
d)
e) Selecting the sample
f)
a)
Collection of data through questionnaires Questionnaire is considered as the heart of survey operation. a) b) General form:
It can be either structured or unstructured. May be either closed or open.
d) e) Question sequence: The question sequence should be clear First few questions are particularly important in seeking
the desired co-operation Questions related to personal character, wealth or memory
of the respondent should be avoided as opening questions
1. 2. 3. 4. 5.
Conducting examination: Obtaining approval from authorities Budgeting Scheduling Emergency care and refferal (diagnostic method)Validity and reliabilty of the data
Classification of study types-ADA(1970) typeI: complete examination typeII: limited examination Type III: inspection Type IV:screening procedures:tongue depressor
d) Analysing the data e)Drawing the conclusion f) Publishing the reports
Case study: it is an intensive investigation of a person, a family, a group, a social institution or an entire community in a natural setting
Correlational study: it is a descriptive research technique utilized to identify consistent relationship among variables
Analytical study Second major type Subject of interest –individual with in population Object –not to formulate but test hypothesis
Can determine: 1.Statistical association between disease and suspected factors 2.If exists--strength
Case control studies
study
Design of a case-control Time
Direction of enquiry Exposed Cases Not Exposed Populat ion Exposed Controls Not Exposed
Defining the cases and controls:
Case: you have to decide a case before the start of the study. The case has to fit in to two criteria.
1. Diagnostic criteria. 2. 3. Eligibility criteria. only newly diagnosed cases within a specified period of time than old cases
Selection of cases The criteria for inclusion in the study must be clearly specified. Sources of cases:
▪ Hospitals 1.
▪ General population
Controls
they must be as similar to the cases as possible, except for the absence of the disease,which is under study.
Selection of controls Crucial step in case-control studies Controls must be ▪ Be similar to the cases except for the absence of the disease under study ▪ Equal ratio
Sources of controls Hospitals:diff illness Relatives
Matching
Definition:
the process by which we select controls in such a way that they are similar to cases with regard to certain pertinent selected variables, which are known to influence the out come of disease and which, if not adequately matched for comparability, could distort or confound the results. Example: age.
Confounding factor One which is associated both with exposure and disease;
and is distributed unequally in study and control groups Although associated with ‘exposure’ under investigation, it
Measurement of exposure
Exposure can be measured by Interviews Questionnaires By studying past records Examinations
Bias/ systematic error should be avoided while measuring the exposure
Analysis Involves two steps 1. Exposure rates among cases and controls 2. Estimation of disease risk associated with exposure (odds ratio)
1. Exposure rates A case control study of smoking and lung cancer
cases Smokers
33 (a)
non Smokers 2 (c) Total
35 (a+c)
55 controls (b) 27 (d) 82 (b+d)
Exposure rate among cases= (a/a+c)100 = (33/35) 100 = 94.2 % Exposure rate among controls= (b/b+d)100 = (55/82) 100 = 67 %
2.Estimation of risk Relative risk (RR) or Risk ratio Relative risk = Incidence among exposed Incidence among non exposed
Smokers Non smokers Total
Cases
Controls
33 (a) 2 (c)
55 (b) 27 (d)
35 (a+c)
82 (b+d)
= a/(a+b)
/
c/(c+d)
Odds ratio (cross product ratio)
It is a key parameter in the analysis of case control studies A measure of the strength of the association between risk factor and outcome Derivation of odds ratio is based on 3 assumptions
Disease under investigation is a rare one Cases are representative of those with disease Controls are representative of those without disease
smokers Non smokers
total
cases 33 (a) 2 (c) 35 (a+c)
55 (b) 27 (d) 82 (b+d)
controls
Odds ratio = ad/bc = 33 X27/ 55X2 = 8.1
Smokers have a risk of having lung cancer 8.1 times that of non smokers
Bias in case control study 1. Bias due to confounding 2. Memory bias 3. Selection bias 4. Berksonians bias:different rates of admission to hosp for people with diff disease 5. Interviewer’s bias 6.
advantages of …
Relatively easy to carry out
Rapid and inexpensive (compared with cohort studies)
Require comparatively few subjects
suitable to investigate rare diseases or diseases about which little is known.
No risk to subjects
Allows the study of several different aetiological factors (e.g., smoking, physical activity and personality characteristics in myocardial infarction)
No attrition problems, because case control studies do not require follow-up of individuals into the future
Ethical problems minimal
Disadvantages of …
High chances for bias
Validation of information obtained is difficult or sometimes impossible
Selection of an appropriate control group may be difficult
We cannot measure incidence, and can only estimate the odds ratio but not relative risk
Not suited to the evaluation of therapy or prophylaxis of a disease
Another major concern is the representativeness of cases and
Cohort studies
Usually undertaken to obtain additional evidence to
refute or support the existence of an association
between suspected cause and disease
Other names
Incidence study
Forward looking study
Longitudinal study
Prospective study
distinguishing Features of …
Cohorts are identified prior to the appearance of the disease under investigation
Study groups are observed over a period of time to determine the frequency of disease
The study proceeds from cause to effect
Cohort is defined as a group of people who share a common characteristic or experience within a defined time period
Eg, birth cohort,age cohorts, occupational cohorts, exposure to a drug cohorts, marriage cohort etc.
The comparison group may be… the general population from which the cohort is
drawn
Indications for …
When there is a good evidence of an association between exposure and disease
When the exposure is rare but the incidence of disease is high among exposed
When the attrition can be minimised
When ample funds are available
of a cohort study Time
Direction of enquiry
Screening to exclude those with the condition
Population free of condition
S A M P L E
With the characteristi c
Develop Disease
a
Do not develop disease
b
Develop Disease
c
Do not
d
Time
Without the characteristi c
Considerations for selecting cohorts
Cohorts must be free from the disease under study
both the groups should be equally susceptible to disease under study
Both the groups should be comparable in respect of all possible variables, except the assumed risk factors
Diagnostic and eligibility criteria of the disease must be defined beforehand.
Inclusion and exclusion criteria should be clearly stated before the commencement
Steps in …
Selection of study subjects
Obtaining data on exposure
Selection of comparison groups
Follow up
Analysis
Selection of study subjects
Cohorts can be selected from General population
Special groups ▪ Select groups (eg. Doctors, lawyers, teachers, etc.) ▪ Exposure groups
Obtaining data on exposure
Information can be obtained from Cohorts Review of records Medical examination or special tests Environmental surveys
Information about exposure should facilitate classification of cohort members According to whether or not they were exposed According to the degree of exposure
Selection of comparison groups
Internal comparisons: no outside comparision group is required
External comparisons: when degree of exposure is not available,ext cohort .eg:smokers and non smokers,radiologists and opthamologists.
Comparison with general population:mortality experience of exposure group is compared with mortality experience of general populationin same geographic area
Follow up
Periodic medical examination of each member
Reviewing physician and hospital records
Routine surveillence of morbidity and mortality records
Mailed questionnaires, telephone interviews, periodic home visits
Analysis
Data is analysed interms of i. Incidence rates of outcome among exposed and nonexposed
ii. Estimation of risk ▪ Relative risk ▪ Attributable risk
Incidence rates
Incidence can be measured directly
Incidence rate among smokers = 70/7000 Yes = 10 per thousand No
Cigarett Lung No lung Total e cancer cancer smoking
Incidence rate among non-smokers= 3/3000 = 1 per 1000
70 a
6930 b
7000 a+b
3 c
2997 d
3000 c+d
Relative risk Cigarett Lung No lung Total e cancer cancer smoking
Relative risThe ratio of incidence among exposed and incidence among non-exposed cid ecalled n ce a m‘risk o n g ratio’ e x p o=se d InAlso
In cid e n ce a m o n g n o n - e x p o se d
10 / 1 = 10
RR=
RR is the direct measure of strength of association
Yes
70 a
6930 b
7000 a+b
No
3 c
2997 d
3000 c+d
RR-i= no assossiation RR > 1= positive assossiation
Attributable risk
The difference in incidence rates between exposed and non-exposed groups
Also called risk difference
Incident rate among exposed – incidence rate among non-exposedX 100 Incident rate among exposed
(10-1/10) X 100 = 90%
of lung cancer was due to their smoking
It indicates to what extent disease can be attributed to the exposure Suggests the amount of disease that might be
Relative risk X Attributable risk
Relative risk Etiological enquiries Larger the RR, stronger the association between risk factor and outcome Does not reflect the potential public health importance
Attributable risk Gives a better idea of the impact of a successful intervention might have in reducing the problem
Advantages of cohort studies
Allow
the
possibility
of
measuring
directly
the relative risk of developing the condition for those who have the characteristic, compared to those who do not
Allows for a conclusion of cause-effect relationship
Because the presence or absence of the risk factor is recorded before the disease occurs, there is no chance of bias
Cohort studies are capable of identifying other diseases that may be related to the same risk factor.
Unlike case-control studies, cohort studies provide
the
possibility of estimating attributable risks, thus indicating the absolute magnitude of
Disadvantages of cohort studies
Not always feasible.
Relatively inefficient for studying rare conditions.
They are very costly in time, personnel, space and patient follow-up.
Sample sizes required for cohort studies are extremely large, especially for infrequent conditions; it is usually difficult to find and manage samples of this size.
The most serious problem is that of attrition, which can affect the validity of the conclusion, if it renders the samples less representative, or if the people who become unavailable are different from those actually followed up. The higher the proportion lost (say beyond 10-15%) the more serious the potential bias.
There may also be attrition among investigators who may lose interest, leave for another job, or become involved in another project.
Over a long period, many changes may occur in the environment, among individuals or in the type of intervention, and these may confuse the issue of association and attributable risk.
Case control study cohort study
Proceeds from effect to cause Starts with the disease Tests whether the suspected exposure occurs more frequently in those with the disease than among those without the disease. Involves fewer number of subjects Yields relatively quick results Suitable for the study of rare diseases Generally yields only estimate of RR (odds ratio) Cannot yield information about diseases other than that selected for study Relatively inexpensive
Proceeds from "cause to effect". Starts with people exposed to risk factor or suspected cause. Tests whether disease occurs more frequently in those exposed, than in those not similarly exposed. Involves larger number of subjects Long follow-up period often needed, involving delayed results. Inappropriate when the disease or exposure under investigation is rare. Yields incidence rates, RR as well as AR. Can yield information about more than one disease outcome. Expensive.
Experimental studies Study of epidemics among colonies of experimental animals such as rats and mice . AIMS
To provide scientific proofs of etiological factors To provide a method of measuring the effectiveness and
efficiency of health services
has all adv and disadv of cohort study and also ethics,cost and feasibility Animal studies: important application Advantages 1. Bred in lab,and can manipulated easily 2. They multiply rapidly Disadvantages: 1. Not all human diseases can be reprodeuced
Human studies: To investigate disease etiology and to evaluate the preventive ,therapeutic measures 1747-john lind-scurvy 1796-Edward Jennar-cowpox
1. Ethical and logistic considerations,benefits weighed againsts the risks involved 2. Volunteers –made fully aware of the experiment 3. WHO (1980)-strict code of practice
Experimental studies
Randomised controlled trials Non-randomized trials
Randomised controlled trials:
Involves some action,interventionor manipulation such as deliberate application or withdrawl of suspected cause.
1. Drawing up a protocal
2.
3. Selecting reference and experimental population
4.
5. Randomization
6.
7. Blinding
8.
9. Manipulation or intervention
D E s i G N o F a N
Select population (Reference or target population)
Select suitable sample (Experimental or study population) Selection by defined criteria Potential participants (Meet selection criteria)
Non-participants (do not meet selection criteria)
Invitation to participate
Non-participants (do not give consent)
Participants Randomization & double blinding
Experimental group Control group
Manipulation, Follow up & Assessment
Positive results: benefit of exp measure----reduced incidence or severity of disease or other appropriate outcomes of study.
Negative results: severity and frequency of side effects and complications ,if any death
Blinding: Randomization cannot guard against these sorts of bias nor the size of the sample.the technique known as blinding is adopted which can be done in Single blind trial: here the participant is not aware whether he belongs to study group or control group. Double blind trial; Here neither the doctor nor the participant is aware of the group
Ethics in research
First important code of ethics was the NURENBURG CODE of 1947. “No research could proceed in human subjects without voluntary consent.”
Declaration of Helsinki code of ethics on principles of ethical behaviour was established in HELSINKII in 1975.
The term “clinical research” to “biomedical research” was revised in HELSINKI- II in 1975
institutional ethics committee or institutional review board
Institutions undertaking clinical trials have to constitute an Institutional Ethics Committee (IEC) or Institutional Review Board (IRB).
It is mandatory that each dissertation research proposal (synopsis) involving humans (irrespective of type of study, including questionnaire based surveys) or animals should be accompanied by a clearance letter from IEC.
ethics and its principles
The science of ideal human character and behavior in situations where distinction must be made between right and wrong, duty must be followed and good inter-personal relations maintained.
When considering the ethical aspect of health research the following principles should also be kept in mind. (Helsinki declaration)
Ethical principles 1. Non-malificence 2. Benificience 3. Veracity or truthfulness 4. Autonomy 5. Justice 6. Confidentiality
submitted to the ethics committee in the following manner 1. Clear research objectives and rationale for
undertaking the investigation in human subjects in the light of existing knowledge.
2. 3. Subject recruitment procedures. 4. 5. Inclusion and exclusion criteria for entry of subjects in the study. 6. 7. Precise description of methodology of the proposed research, including intended dosage of drugs,
5. A description of plans to withdraw or withhold standard therapies in the course of research. 6. 7. The plans for statistical analysis of the study. 8. 9. Procedure for seeking and obtaining informed consent with sample of patient information sheet and informed consent forms in English and regional languages. 10. 11.Safety of proposed intervention and any drug or
9. For research carrying more than minimal risk, an account of plans to provide medical therapy for such risk or injury or toxicity due to over dosage should be included. 10.Proposed compensation and reimbursement of incidental expenses.
11.
12.Storage and maintenance of all data collected during the trial.
13.
14.Plans for publication of results- positive or negative- while maintaining the privacy and confidentiality of the study participants.
Considerations to be kept in mind while conducting research: In any research on human beings, each subject must be adequately informed of the aim, methods, anticipated benefits and potential hazards of the study and the discomfort it may entail.
When obtaining informed consent, we should be cautious if the subject has a dependent relationship to us. No pressure or threat should be exercised.
In case of legal incompetence informed consent should be obtained from the legal guardian in accordance with the existing legislation.
references Behavioural sciences for dentistry. G.Humphris & M.S.Ling. Churchill Livingstone.2000.
Health research methodology- a guide for training in research methods. WHO 1992
Critical thinking; understanding and evaluating dental research. D.M.Brunette. Quintessence publishing. 1996.
Dentistry, dental practice and community. 5th edition. B.A. Burt & S.A.Eklund. WB Saunders company.
Park’s text book of preventive and social medicine. 19th edition. K.Park. Bhanot publishers. 2007.
TH A N K YO U
contents Introduction to research Definitions Research Thesis Dissertation Why to do a research Categories of research Research methods & research methodology Procedural steps in research Research strategy epidemiologic studies
Introduction
Investigation using scientific procedures, by searching again and again to find out the truth
Research is the continual search for truth using the scientific method. It is the pursuit of the truth with the help of study, investigation, observation, comparison and/or
definitions
Research (WHO Health research methodology, 1992, a guide for training in research methods):
Research is a quest for knowledge through diligent search or investigation or experimentation aimed at the discovery and interpretation of new knowledge. Scientific method is a systematic body of procedures and techniques applied in carrying out investigation or experimentation targeted at obtaining new knowledge. Here research and scientific methods may be considered a course of critical enquiry leading to discovery of facts or information which increases
Thesis
(according to Oxford English dictionary)
A proposition laid down as a theme to be discussed and proved. A discussion to maintain and prove a thesis especially written or delivered by a candidate for university degree- Ph.D
Dissertation:
Dissertation means “to discuss”. It is an academic activity laid down by the partial fulfillment of MDS
university for the
degree.
It is an exercise to train a PG student to plan, execute, evaluate, write and report a scientific project. It is an in-depth study of a particular topic which contributes new information and knowledge in the field A formal, often lengthy treatise (a book or writing of some particular subject, one containing a methodical discussion or exposition of principles of subject) or discourse, especially one
It is a pre-requisite or academic activity for acquiring a masters degree or doctorial.
To find out the truth which is hidden and which has not been discovered yet.
To contribute new knowledge to the existing one as the scientific knowledge develops in increments.
As a profession to conduct research in various aspects.
To solve an existing health problem.
Categories of research
1.
Empirical research and theoretical research Basic research and Applied research
Empirical
Observational research
Experimental research
Basic or pure research
It is usually considered to involve the search for knowledge without a defined goal of utility or specific purpose.
Eg. The microbiologist, whose expertise is the identification of pathogenic micro organisms may conduct research in-vitro, in a laboratory on bacterial reproduction, growth and endotoxin production without any direct application to clinical dentistry. Probably, the researcher is interested in monitoring endotoxins produced over the life cycle of bacteria to determine a pathogenecity.
Applied research
It is problem oriented and is directed towards a defined and purposeful end.
Eg. An oral health researcher investigating the relationship between periodontal disease and myocardial infarction may use the findings of the microbiologist as a theoretical framework to test the relationship between bacterial endotoxins, periodontal disease and myocardial infarction in animal and then in human subjects
Research methods
methods/ techniques that are used for conducting research are termed as research methods or research techniques.
1. 2.
3.
They fall into 3 groups 1. Those concerned with collection of data 2. Those statistical techniques which are used for establishing relationship between the data and the unknown
Research methodology
It is a way to systematically solve the research problem. It is necessary for the researcher to design his methodology for his problem, as the same may differ from problem to problem i.e. 1.
2. Why a research study has been undertaken 3. 4. How the research problem has been defined 5. 6. In what way and why the hypothesis has been formed
4. 5.
4. What data has been collected 5. What particular method has been adopted for collection of data 6. Why a particular technique of data collection has been used
And a host of similar questions are usually answered when we talk of research methodology, so that research results are capable of being evaluated either by the researcher himself or by others
Procedural steps in research
Selection of problem for investigation-further exploration Inexperienced-seek opinion –senior Constructing –essential starting point
Review literature Modern electronic research Abstract collection held on CD-ROMS-enables –key words Medline and psyclit database Role of systemic review grown recently-cochrane collaborationreviews from volunteer researchers internationally adds them to a bank,which is open for inspection by interesting parties.
Specifying study design
Selection of measures: many measure ,assessments Eg:self report rating scales for dental anxiety,observations,interviews,stand questionnaires
simple rating scale can be given a no.1-strongly agree 2-agree 3-undecided 4-disagree 5-strongly disgree May not exist for the study ,this may necessiate the development of new scale. should possess Reliability and validity
Selection of sample:
Sampling techniques-inorder to provide information ,can be generalised to cover the whole population.
Writing a protocol: aims & objectives,method,materials,sample ,procedure
Ethical approval Pilot work Main study Analysis of results Report writing publication
Research strategies Selection
of a research strategy is the core of a research design and is probably the single most Important decision the investigator has to make, i.e. whether to undertake a descriptive, an analytical or an experimental study.
Classification of Epidemiologic studies
Decscriptive study
Concerned with observing the distribution of disease or health related characteristics in human population Eg. Surveys. Defining population:denominator Defining the disease:operational definition. Describing disease-time,place and person Time: Short term fluctuation: 1. Common source epidemics-single,continuous 2. Propagated epidemics-person to person transmission of infectious agent---epidemics of hepatitis A and poliomyelitis
Periodic fluctuations: Seasonal –communicable diseases like measles,varicella,malaria Eg:upper Resp tract infections inc during winter and GI inf in summer Cyclic trends-measles-incidence every 2-3 yrs Influenza occurs at intervals of 7-10 yrs Long term fluctuation Changes occur over long period of time,change in frequency encompassing sev decades Eg:CHD,diabetes,lung cancer shows upward trend in 50 decades and TB, typhoid downward
Place distribution: Interanational National-endemic disease like goitre,flourosis Rural-urban-lung cancer,cardiovascular accidents-urban
Person distribution:age sex Measurement of disease :morbidity and mortality indicators
Expressed in terms of incidence and prevalence
Comparing with known indices:comparision b/n different population and subgroups of same populn-clue to etiology Formulation of hypothesis:relating to disease etiology specify-population,sp cause ,expected outcome,dose-response r/n,time-resp r/n. Eg:smoking of 30-40 cigarettes/day causes lung cancer in 10% of smokers after 20 yrs of exposure. Uses: 1. magnitude and type of disease in community 2. Clues to etiology 3. contributes to research
surveys
Surveys are methods of scientific or systematic collection of data, compiling, presenting in order (useful manner), analysing and evaluating them
The focus of attention must be on the following a) Formulating the objective of the study-obj describing what is to be measured,resources
b)
c) Designing the method of data collection eg. Questionnaires, interviewing, examination of records or observations
d)
e) Selecting the sample
f)
a)
Collection of data through questionnaires Questionnaire is considered as the heart of survey operation. a) b) General form:
It can be either structured or unstructured. May be either closed or open.
d) e) Question sequence: The question sequence should be clear First few questions are particularly important in seeking
the desired co-operation Questions related to personal character, wealth or memory
of the respondent should be avoided as opening questions
1. 2. 3. 4. 5.
Conducting examination: Obtaining approval from authorities Budgeting Scheduling Emergency care and refferal (diagnostic method)Validity and reliabilty of the data
Classification of study types-ADA(1970) typeI: complete examination typeII: limited examination Type III: inspection Type IV:screening procedures:tongue depressor
d) Analysing the data e)Drawing the conclusion f) Publishing the reports
Case study: it is an intensive investigation of a person, a family, a group, a social institution or an entire community in a natural setting
Correlational study: it is a descriptive research technique utilized to identify consistent relationship among variables
Analytical study Second major type Subject of interest –individual with in population Object –not to formulate but test hypothesis
Can determine: 1.Statistical association between disease and suspected factors 2.If exists--strength
Case control studies
study
Design of a case-control Time
Direction of enquiry Exposed Cases Not Exposed Populat ion Exposed Controls Not Exposed
Defining the cases and controls:
Case: you have to decide a case before the start of the study. The case has to fit in to two criteria.
1. Diagnostic criteria. 2. 3. Eligibility criteria. only newly diagnosed cases within a specified period of time than old cases
Selection of cases The criteria for inclusion in the study must be clearly specified. Sources of cases:
▪ Hospitals 1.
▪ General population
Controls
they must be as similar to the cases as possible, except for the absence of the disease,which is under study.
Selection of controls Crucial step in case-control studies Controls must be ▪ Be similar to the cases except for the absence of the disease under study ▪ Equal ratio
Sources of controls Hospitals:diff illness Relatives
Matching
Definition:
the process by which we select controls in such a way that they are similar to cases with regard to certain pertinent selected variables, which are known to influence the out come of disease and which, if not adequately matched for comparability, could distort or confound the results. Example: age.
Confounding factor One which is associated both with exposure and disease;
and is distributed unequally in study and control groups Although associated with ‘exposure’ under investigation, it
Measurement of exposure
Exposure can be measured by Interviews Questionnaires By studying past records Examinations
Bias/ systematic error should be avoided while measuring the exposure
Analysis Involves two steps 1. Exposure rates among cases and controls 2. Estimation of disease risk associated with exposure (odds ratio)
1. Exposure rates A case control study of smoking and lung cancer
cases Smokers
33 (a)
non Smokers 2 (c) Total
35 (a+c)
55 controls (b) 27 (d) 82 (b+d)
Exposure rate among cases= (a/a+c)100 = (33/35) 100 = 94.2 % Exposure rate among controls= (b/b+d)100 = (55/82) 100 = 67 %
2.Estimation of risk Relative risk (RR) or Risk ratio Relative risk = Incidence among exposed Incidence among non exposed
Smokers Non smokers Total
Cases
Controls
33 (a) 2 (c)
55 (b) 27 (d)
35 (a+c)
82 (b+d)
= a/(a+b)
/
c/(c+d)
Odds ratio (cross product ratio)
It is a key parameter in the analysis of case control studies A measure of the strength of the association between risk factor and outcome Derivation of odds ratio is based on 3 assumptions
Disease under investigation is a rare one Cases are representative of those with disease Controls are representative of those without disease
smokers Non smokers
total
cases 33 (a) 2 (c) 35 (a+c)
55 (b) 27 (d) 82 (b+d)
controls
Odds ratio = ad/bc = 33 X27/ 55X2 = 8.1
Smokers have a risk of having lung cancer 8.1 times that of non smokers
Bias in case control study 1. Bias due to confounding 2. Memory bias 3. Selection bias 4. Berksonians bias:different rates of admission to hosp for people with diff disease 5. Interviewer’s bias 6.
advantages of …
Relatively easy to carry out
Rapid and inexpensive (compared with cohort studies)
Require comparatively few subjects
suitable to investigate rare diseases or diseases about which little is known.
No risk to subjects
Allows the study of several different aetiological factors (e.g., smoking, physical activity and personality characteristics in myocardial infarction)
No attrition problems, because case control studies do not require follow-up of individuals into the future
Ethical problems minimal
Disadvantages of …
High chances for bias
Validation of information obtained is difficult or sometimes impossible
Selection of an appropriate control group may be difficult
We cannot measure incidence, and can only estimate the odds ratio but not relative risk
Not suited to the evaluation of therapy or prophylaxis of a disease
Another major concern is the representativeness of cases and
Cohort studies
Usually undertaken to obtain additional evidence to
refute or support the existence of an association
between suspected cause and disease
Other names
Incidence study
Forward looking study
Longitudinal study
Prospective study
distinguishing Features of …
Cohorts are identified prior to the appearance of the disease under investigation
Study groups are observed over a period of time to determine the frequency of disease
The study proceeds from cause to effect
Cohort is defined as a group of people who share a common characteristic or experience within a defined time period
Eg, birth cohort,age cohorts, occupational cohorts, exposure to a drug cohorts, marriage cohort etc.
The comparison group may be… the general population from which the cohort is
drawn
Indications for …
When there is a good evidence of an association between exposure and disease
When the exposure is rare but the incidence of disease is high among exposed
When the attrition can be minimised
When ample funds are available
of a cohort study Time
Direction of enquiry
Screening to exclude those with the condition
Population free of condition
S A M P L E
With the characteristi c
Develop Disease
a
Do not develop disease
b
Develop Disease
c
Do not
d
Time
Without the characteristi c
Considerations for selecting cohorts
Cohorts must be free from the disease under study
both the groups should be equally susceptible to disease under study
Both the groups should be comparable in respect of all possible variables, except the assumed risk factors
Diagnostic and eligibility criteria of the disease must be defined beforehand.
Inclusion and exclusion criteria should be clearly stated before the commencement
Steps in …
Selection of study subjects
Obtaining data on exposure
Selection of comparison groups
Follow up
Analysis
Selection of study subjects
Cohorts can be selected from General population
Special groups ▪ Select groups (eg. Doctors, lawyers, teachers, etc.) ▪ Exposure groups
Obtaining data on exposure
Information can be obtained from Cohorts Review of records Medical examination or special tests Environmental surveys
Information about exposure should facilitate classification of cohort members According to whether or not they were exposed According to the degree of exposure
Selection of comparison groups
Internal comparisons: no outside comparision group is required
External comparisons: when degree of exposure is not available,ext cohort .eg:smokers and non smokers,radiologists and opthamologists.
Comparison with general population:mortality experience of exposure group is compared with mortality experience of general populationin same geographic area
Follow up
Periodic medical examination of each member
Reviewing physician and hospital records
Routine surveillence of morbidity and mortality records
Mailed questionnaires, telephone interviews, periodic home visits
Analysis
Data is analysed interms of i. Incidence rates of outcome among exposed and nonexposed
ii. Estimation of risk ▪ Relative risk ▪ Attributable risk
Incidence rates
Incidence can be measured directly
Incidence rate among smokers = 70/7000 Yes = 10 per thousand No
Cigarett Lung No lung Total e cancer cancer smoking
Incidence rate among non-smokers= 3/3000 = 1 per 1000
70 a
6930 b
7000 a+b
3 c
2997 d
3000 c+d
Relative risk Cigarett Lung No lung Total e cancer cancer smoking
Relative risThe ratio of incidence among exposed and incidence among non-exposed cid ecalled n ce a m‘risk o n g ratio’ e x p o=se d InAlso
In cid e n ce a m o n g n o n - e x p o se d
10 / 1 = 10
RR=
RR is the direct measure of strength of association
Yes
70 a
6930 b
7000 a+b
No
3 c
2997 d
3000 c+d
RR-i= no assossiation RR > 1= positive assossiation
Attributable risk
The difference in incidence rates between exposed and non-exposed groups
Also called risk difference
Incident rate among exposed – incidence rate among non-exposedX 100 Incident rate among exposed
(10-1/10) X 100 = 90%
of lung cancer was due to their smoking
It indicates to what extent disease can be attributed to the exposure Suggests the amount of disease that might be
Relative risk X Attributable risk
Relative risk Etiological enquiries Larger the RR, stronger the association between risk factor and outcome Does not reflect the potential public health importance
Attributable risk Gives a better idea of the impact of a successful intervention might have in reducing the problem
Advantages of cohort studies
Allow
the
possibility
of
measuring
directly
the relative risk of developing the condition for those who have the characteristic, compared to those who do not
Allows for a conclusion of cause-effect relationship
Because the presence or absence of the risk factor is recorded before the disease occurs, there is no chance of bias
Cohort studies are capable of identifying other diseases that may be related to the same risk factor.
Unlike case-control studies, cohort studies provide
the
possibility of estimating attributable risks, thus indicating the absolute magnitude of
Disadvantages of cohort studies
Not always feasible.
Relatively inefficient for studying rare conditions.
They are very costly in time, personnel, space and patient follow-up.
Sample sizes required for cohort studies are extremely large, especially for infrequent conditions; it is usually difficult to find and manage samples of this size.
The most serious problem is that of attrition, which can affect the validity of the conclusion, if it renders the samples less representative, or if the people who become unavailable are different from those actually followed up. The higher the proportion lost (say beyond 10-15%) the more serious the potential bias.
There may also be attrition among investigators who may lose interest, leave for another job, or become involved in another project.
Over a long period, many changes may occur in the environment, among individuals or in the type of intervention, and these may confuse the issue of association and attributable risk.
Case control study cohort study
Proceeds from effect to cause Starts with the disease Tests whether the suspected exposure occurs more frequently in those with the disease than among those without the disease. Involves fewer number of subjects Yields relatively quick results Suitable for the study of rare diseases Generally yields only estimate of RR (odds ratio) Cannot yield information about diseases other than that selected for study Relatively inexpensive
Proceeds from "cause to effect". Starts with people exposed to risk factor or suspected cause. Tests whether disease occurs more frequently in those exposed, than in those not similarly exposed. Involves larger number of subjects Long follow-up period often needed, involving delayed results. Inappropriate when the disease or exposure under investigation is rare. Yields incidence rates, RR as well as AR. Can yield information about more than one disease outcome. Expensive.
Experimental studies Study of epidemics among colonies of experimental animals such as rats and mice . AIMS
To provide scientific proofs of etiological factors To provide a method of measuring the effectiveness and
efficiency of health services
has all adv and disadv of cohort study and also ethics,cost and feasibility Animal studies: important application Advantages 1. Bred in lab,and can manipulated easily 2. They multiply rapidly Disadvantages: 1. Not all human diseases can be reprodeuced
Human studies: To investigate disease etiology and to evaluate the preventive ,therapeutic measures 1747-john lind-scurvy 1796-Edward Jennar-cowpox
1. Ethical and logistic considerations,benefits weighed againsts the risks involved 2. Volunteers –made fully aware of the experiment 3. WHO (1980)-strict code of practice
Experimental studies
Randomised controlled trials Non-randomized trials
Randomised controlled trials:
Involves some action,interventionor manipulation such as deliberate application or withdrawl of suspected cause.
1. Drawing up a protocal
2.
3. Selecting reference and experimental population
4.
5. Randomization
6.
7. Blinding
8.
9. Manipulation or intervention
D E s i G N o F a N
Select population (Reference or target population)
Select suitable sample (Experimental or study population) Selection by defined criteria Potential participants (Meet selection criteria)
Non-participants (do not meet selection criteria)
Invitation to participate
Non-participants (do not give consent)
Participants Randomization & double blinding
Experimental group Control group
Manipulation, Follow up & Assessment
Positive results: benefit of exp measure----reduced incidence or severity of disease or other appropriate outcomes of study.
Negative results: severity and frequency of side effects and complications ,if any death
Blinding: Randomization cannot guard against these sorts of bias nor the size of the sample.the technique known as blinding is adopted which can be done in Single blind trial: here the participant is not aware whether he belongs to study group or control group. Double blind trial; Here neither the doctor nor the participant is aware of the group
Ethics in research
First important code of ethics was the NURENBURG CODE of 1947. “No research could proceed in human subjects without voluntary consent.”
Declaration of Helsinki code of ethics on principles of ethical behaviour was established in HELSINKII in 1975.
The term “clinical research” to “biomedical research” was revised in HELSINKI- II in 1975
institutional ethics committee or institutional review board
Institutions undertaking clinical trials have to constitute an Institutional Ethics Committee (IEC) or Institutional Review Board (IRB).
It is mandatory that each dissertation research proposal (synopsis) involving humans (irrespective of type of study, including questionnaire based surveys) or animals should be accompanied by a clearance letter from IEC.
ethics and its principles
The science of ideal human character and behavior in situations where distinction must be made between right and wrong, duty must be followed and good inter-personal relations maintained.
When considering the ethical aspect of health research the following principles should also be kept in mind. (Helsinki declaration)
Ethical principles 1. Non-malificence 2. Benificience 3. Veracity or truthfulness 4. Autonomy 5. Justice 6. Confidentiality
submitted to the ethics committee in the following manner 1. Clear research objectives and rationale for
undertaking the investigation in human subjects in the light of existing knowledge.
2. 3. Subject recruitment procedures. 4. 5. Inclusion and exclusion criteria for entry of subjects in the study. 6. 7. Precise description of methodology of the proposed research, including intended dosage of drugs,
5. A description of plans to withdraw or withhold standard therapies in the course of research. 6. 7. The plans for statistical analysis of the study. 8. 9. Procedure for seeking and obtaining informed consent with sample of patient information sheet and informed consent forms in English and regional languages. 10. 11.Safety of proposed intervention and any drug or
9. For research carrying more than minimal risk, an account of plans to provide medical therapy for such risk or injury or toxicity due to over dosage should be included. 10.Proposed compensation and reimbursement of incidental expenses.
11.
12.Storage and maintenance of all data collected during the trial.
13.
14.Plans for publication of results- positive or negative- while maintaining the privacy and confidentiality of the study participants.
Considerations to be kept in mind while conducting research: In any research on human beings, each subject must be adequately informed of the aim, methods, anticipated benefits and potential hazards of the study and the discomfort it may entail.
When obtaining informed consent, we should be cautious if the subject has a dependent relationship to us. No pressure or threat should be exercised.
In case of legal incompetence informed consent should be obtained from the legal guardian in accordance with the existing legislation.
references Behavioural sciences for dentistry. G.Humphris & M.S.Ling. Churchill Livingstone.2000.
Health research methodology- a guide for training in research methods. WHO 1992
Critical thinking; understanding and evaluating dental research. D.M.Brunette. Quintessence publishing. 1996.
Dentistry, dental practice and community. 5th edition. B.A. Burt & S.A.Eklund. WB Saunders company.
Park’s text book of preventive and social medicine. 19th edition. K.Park. Bhanot publishers. 2007.
TH A N K YO U
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