Study Designs

Study Designs A Presentation

Types of Study designs • Non Intervention Studies Descriptive studies Comparative (analytical) studies Exploratory studies

• Intervention Studies The two categories of intervention studies are:

Experimental studies Quasi-experimental studies.

Current Classification D

3 4

E

. .

P I D

I P

I O

R

1

.

C

a

s

e

R

e

p O o B r tS

2

.

C

a

s

e

S

e

r i e s C A S

r o

r r e

l a

s

S

s

I V

M

C

o

T

E

S

C C

E

e

L O

E

t i o

n

c

t i o

A

/

E C n

E

R

a

O

l

o H

/

N

O

I C

A

V

E c

G

A

L

T

A

Y

T

L I C

A

L

I EO X N P A E L R

C

O

N

T 1 R . O S Li n

l o

g

i c

a

P

S

I M g

l e

l

R T 2 . D o u r e v a l e n c e 3

.

T

r i p

b

l

l e

Descriptive Studies Descriptive studies involve the systematic collection and presentation of data to give a clear picture of a particular situation and can be carried out on a small or large scale.

• Case studies • Case series

Comparative or Analytical Studies • An ANALYTICAL STUDY attempts to establish causes or risk factors for certain problems. This is done by comparing two or more groups, some of which have or develop the problem and some of which have not.

Cross-sectional Comparative studies • Many cross-sectional surveys focus on comparing as well as describing groups.

• For example, a survey on malnutrition may wish to establish:

 The percentage of malnourished children in a certain population  Socioeconomic,physical,political variables that influence the availability of food

Cross Sectional Surveys Quantify the distribution of certain variables in a study population at a point of time. They may cover, for example:

• Physical characteristics of people, materials, or the

environment,etc • The behavior of people and the knowledge, attitudes, beliefs, and opinions that may help to explain that behaviour (KAP studies), or events that occurred in the population. • Cross-sectional surveys cover a sample of the population. If a cross-sectional study covers the total population it is called a census.

Case Control Studies • In a CASE-CONTROL STUDY, the investigator compares one group among whom a problem is (e.g., malnutrition) with another group, called a control or comparison group, where the problem is absent to find out what factors have contributed to the problem.

Odds Ratio (OR) • Measure of the strength of the association between risk factor and outcome. • The derivation of the Odds Ratio is based on three assumptions: - The disease being investigated must be relatively rare. - The cases must be representative of those with the disease - The controls must be representative of those without disease

Cohort Studies • In a COHORT STUDY, a group of individuals that

is exposed to a risk factor (study group) is compared with a group of individuals not exposed to the risk factor (control group).

• The researcher follows both groups over time and

compares the occurrence of the problem that he or she expects to be related to the risk factor in the two groups to determine whether a greater proportion of those with the risk factor are indeed affected.

Relative Ratio (RR) • Ratio of incidence of the disease (or death)among exposed and the incidence among non-exposed.

• It is a direct measure (or index) of the “strength” of the association between suspected cause and effect

Exploratory Studies • An Exploratory study is a small-scale study of relatively which is carried out is known about a problem.

short duration, when little else situation or a

Intervention Studies • In intervention studies, the researcher

manipulates a situation and measures the effects of the manipulation. Usually (but not always) two groups are compared, one in which the intervention takes place (e.g.. treatment with a certain drug) and another group that remains "untouched" (e.g., treatment with a placebo) .

Experimental Studies • Experimental design is the only type of study design that can actually prove causation.

• In an EXPERIMENTAL STUDY, individuals are randomly allocated to at least two groups. One group is subjected to an intervention or experiment, while the other group(s) is not.

• The outcome of the intervention - effect of the intervention on the dependent (variable/problem) is obtained by comparing the two groups.

Classical Experimental Study Design The classical experimental study design has three characteristics:

• Manipulation • Control • Randomization

Quasi – Experimental Studies • In a QUASI-EXPERIMENTAL STUDY, at least one characteristic of a true experiment is missing.

• One

of the most common quasiexperimental designs uses two (or more) groups, one of, which serves a control group in which no intervention takes place.

• Both groups are observed before as well as after the intervention, to test if the intervention has made any difference.