Prevalence Survey

Prevalence survey

descriptive study Descriptive study includes activities relates to characterizing the distribution of disease within a population. descriptive patterns of disease occurrence often lead to hypotheses about disease causation that are tested in analytic investigations.

Prevalence studies are conducted in order to examine the prevalence of a particular condition at a certain point in time. Also referred to as cross-sectional studies, they frequently take the form of surveys.

prevalence survey     

cross-sectional study,is also named crosssectional an frequently used- investigation methods of epidemiology is basis and starting point of research of epidemiology is standpoint of public health policy An important epidemic investigating method

Prevalence survey 







section Ⅰ introduce of prevalence survey section Ⅱ methods and kinds of prevalence survey section Ⅲ carrying procedure of prevalence survey section Ⅳ bias and that of control of prevalence survey

section Ⅰ introduce of prevalence survey 

1. concept prevalence survey,an analytic investigation in which subjects are sampled at a fixed point or period of time,and the associations between the concurrent presence or absence of risk factors and disease are then investigated.

2. feature of prevalence survey   

 

Detailed,rapid and cheap According to cross-sectional study Only put forword to hypothesis of pathogenesis Often be used to research chronic disease Be more applicable to the research of disease whose exposure factor dose not change easily

3. research aim of prevalence survey      

To describe distribution of disease To discovery clue of pathogenesis Be used in secondary prevention To evaluate prevention and cure effect surveillance of disease health demand,health project and health policy decision

section Ⅱ methods and kinds of prevalence survey

1.Methods of prevalence survey      

visit face to face visit by message visit by telephone questionnaire physical examination and lab examination investigation with IE

Methods of prevalence survey 

Investigation methods of sensitive problem 



sensitive problem

Two kinds 

attributive sensitive problem



quantity sensitive problem

 

2. Kinds of prevalence survey census sampling survey

census 



Investigation in special time and special extend object 



To discovery and cure patients in early stage To understand distribution of disease and health condition

census 

principal 

  

need to have organize and high level census team need to have time request data need to put together According to specific cycle

census 

Merit   

investigated object is easy data is detailed and has high accuracy To help research epidemic factors of diseases

census  

weakness amount of work is big,cost is high and organized work is different   

investigated content is limited repetition and leakage Investigated accuracy controlled difficultly

sampling survey



To research the subset which of a target population that is chosen for investigation Prevalence survey often adopts method of sampling survey

sampling survey 

principal 



Sampling survey must abide by randomization Sample size must be big enough to represent totality

sampling survey 

Merit  





abide by randomization save labor power, material resources and time Error may be evaluated and controlled in advance Accuracy is high

sampling survey 

weakness   

A non-total investigation method sampling error and bias Can not be used in disease of lowprevalence rate

sampling survey 

sampling methods ：     

simple random sampling systematic sampling stratified sampling cluster sampling multi-stage sampling

sampling survey 

sample size   

αvalue prevalence rate or standard divergence ； Admitting error

sample size ： 

①quantitative data ： d - error S - sd



②enumeration data ： prevalence ，

P-prevalence Q=1-P

Section Ⅲ steps of prevalence survey 

1. Determine research object 





To describe distribution, explore pathogenesis and build normal value To reflect practice,creativity,science and advance

2. To grasp data of background 

Experience of own,consulting with expert and looking up reference data



3. Determine research object and methods 

  

objects ： persons at risk, occupational population, representative population, population carried out prevention or cure measurement. census, screening, sampling survey. Research methods sample size ：



4.Determine research types and methods

   

According to object considering speciality of data thinking over feature of object



5.collection of data 



1.Determine research variable ： including data of demographic, disease measurements and relative factors 2.questionnaire

   

To grasp data of background disease measure exposure measure demand of investigator



6.Data analysis and explanation of result 

data examination ：   

program examination data examination logic examination



data analysis (1)analysis measurement ： numerical variable ： arithmetic mean 、 standard deviation 、 95%confidence interval 。  categorical variable ： rate 、 proportion 。 

(2)analysis methods ：  descriptive

distribution  relative analysis  one factor comparison analysis  multiple factors analysis

(3) Explanation of result

To state representative sample,sample reliability and estimate the sourse 、 size 、 direction and method of adjustment

Section Ⅳ common bias and control 

Selection bias   

non-respondent bias selection bias survival bias



Information bias   

report bias ； investigator bias ； Measurement instrument 、 appliance

bias ：

Section Ⅳ common bias and control 

control of bias    

randomization increase respond rate control measurement bias avoid investigator bias

Some advantages and disadvantages of prevalence studies 

Advantages



Disadvantages



Comparatively cheap and quick Fairly simple to carry out and analysis Useful for healthcare planning and investigating trends over time Useful when routine data are not available



Not useful for conditions which have a short duration Not a first choice for investigating causality Sampling and data collection need great care

 





