Dear Dr. Nantha

I think that you need to provide a little more context of what it is you want to measure of prevalence of. The prevalence (of some state) can be estimated with a variety of different design, including cohort studies. But it all depends on the details.

The standard study design for measuring prevalence is a survey.

Cohort study can identify risk. For population prevalence, best study will be cross sectional.

thanks.

The best design to estimate prevalence is a cross-sectional survey (for point prevalence) or survey over a period of time (period prevalence).  But your cohort can still be informative because it identifies prevalence within a defined group. For example if your cohort is mostly people in a certain age range or with certain medical conditions, then the prevalence of the disease in this group can be important to know.  If your cohort is composed entirely of diabetic people for example, and you look at the prevalence of eye disease in this cohort, then the cohort may give a more accurate picture of the prevalence (and the incidence) of eye disease among diabetics than you would get by sampling the population at large and seeing how many people have both diabetes and eye disease.  Of course, you're missing the denominator with a cohort (i.e., you wouldn't know the basic diabetic rate in the general population) unless your cohort represents a good statistical cross-section of the population, or is composed of the entire subpopulation of people who get the disease (e.g. all children in a province with blindness or all deaths from traffic accidents, where you can assume there is complete ascertainment of all cases and all cases are in your retrospective cohort). 

Hi, hope this helps.

https://en.wikipedia.org/wiki/Prevalence

At least it's not the problem of cohort design. Perhaps more information about your research question vs. your results should be provided here.

Best,

shihua

I think that you need to ask whether the retrospective cohort is representative of the group for which you want to estimate prevalence. Absent representativeness, it will be difficult to generalize prevalence for the population from which the sample was drawn.

Cohort studies cannot provide answers to prevalence. It is basically used to identify risk and quantify it. Crossectional studies answer prevalence question.

I think you can calculate prevalence ratio in a cohort study. 

Therefore, Prevalence Ratio (which is falsely called Prevalence Rate Ratio- because prevalence is not a rate) indicates how large is the prevalence of an event/outcome in one group of subject with  a certain characteristics relative to another group (without the characteristics), but the difference it is in a point in time, so follow up time is not important, unless you are doing period prevalence. 

At any point in time in a cohort you can do a cross sectional analysis, but not sure if this has valuable information to give you  compared to risk ratio and OR.

But for prevalence of a disease which is  to measure the proportion of certain outcome or disease in a point in time, a cross sectional design is better, so here it's different you are not comparing exposed and non exposed. So not sure, which one you want to choose. In cohort design as I discussed above you can calculate the prevalence ratio 

HI, 

You can calculate prevalence if you calculate incidence. Kleinbaum  explainin his book EPIDEMIOLOGIC RESEARCH; principles and Quantitative methods, pag 121. Where he say how we can calculate prevalence by incidence. P= ID/ ID+TD...TD is the termination rate (or density). I hope this can help you. 

From Cohort study u can calculate the following things:

Incidence

Relative risk / Risk ratio

Attributable risk

Prevalence - till period of followup number of new and old cases divided by whole population

Details of the study design is important to decipher this issue. How was a sample size calculated, if ratio( of for instance normal to abnormal ) was inputted then certainly prevalence determination would not be appropriate.

It would be better to also consider main objective. If prevalence is a main objective then it is appropriate to consider a cross sectional comparative study which has the advantage of providing prevalence and any comparisons factors so to speak.

Thanks

you can calculate the the period prevalence if the number of population is specified over your follow up period.It can be used in a condition by specifying a certain point in time at the end of the follow up and use retrospective-cross sectional design

cross-sectional study is the best to estimate the prevalence