Is it commendable or possible to computing and describing the prevalence rate of an outcome interest (mainly the cases) in case control study? I hope the answer whould be yes. However, I am confusing that in a case control study the respondents were selected from the source population which we are targeting based on the case ness or non case-ness conditions. Already the cases were known and and no more computing prevalence in the course of the study. How eve,r I think, we can comput it by taking assumptions of howmony of cases are found from the tareget population and ready for sam,pling procedure. Meaning we can determine before the study was conducted.Thus, in such cases what is the need to compute or present the revalence since it was not assumed as key findings in the research process? If you your suggestion is yes how can estimate the prevalence? In which case can we compute it?
Thank you in advance for your quick response and genuen answers!
There are two separate issues here. Prevalence of a condition is a descriptive quantity descibing the proportion of the population affected at a fixed point in time (or over a defined period).It can be determined exactly if you know the total population size and can ascertain the total no. affected in the population.With some registers this can be done. Otherwise you need a random sample of the population to estimate prevalence.
A case control study on the other hand is an analytical study to determine the relative risk (incidence rate ratio) between those exposed to a risk factor and those not exposed To do this you obtain some incident cases from the source population, not necessarily randomly sampled and compare their exposure status to that of referent (controls) which must be sampled independently of exposure from the source population which generated the cases..
the relative numbers of exposed and unexposed controls gives the relative sizes of the exposed and unexposed source populations.
It would only be under exceptional conditions that a case control study based on prevalent cases could determine incidence rate ratio eg same average duration of disease in exposed and non exposed, no migration into or out of prevalence pool,
If you were assembling incident cases from a defined population of known size and you followed these cases over time then you could calculate prevalence at any time point or over any chosen period.
You may calculate the proportion, provided you do a nested case control study as you will have a cohort which you will have to follow up prospectively, thereby you can calculate the propotion of cases. Thereafter, you may do a case control study after the outcome of interest has occured in that particular cohort.
Alternate to this design is case-cohort study.
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