As a journal editor i used to see the manuscripts with Incidence and Prevalence for the studies with sample size 20, 30, 100 etc. Is it better to use percentage or pattern instead of Incidence, Prevalence with these type of studies? How to stop the miss use of Incidence, Prevalence in Medical Journals?.
The reporting of incidence versus prevalence depends on the question you are attempting to answer. If you are concerned simply with the proportion of cases in a population at a given time, you are interested in reporting the prevalence. If, in contrast, you want to know how many new cases are arising in a population - for instance, if you are tracking the spread of infectious disease - you are concerned with incidence.
The reporting of incidence versus prevalence depends on the question you are attempting to answer. If you are concerned simply with the proportion of cases in a population at a given time, you are interested in reporting the prevalence. If, in contrast, you want to know how many new cases are arising in a population - for instance, if you are tracking the spread of infectious disease - you are concerned with incidence.
Actually, incidence and prevalence are not related to sample size and are very different from just a percentage. They depend on how you select subject with disease or other condition for your study. If you select individual randomly insofar they can represent total population, (i.e your sample is representative of population for which you want to draw conclusion) then your calculated percentage is called prevalence. But if you have density sampling i.e every healthy individual are followed until they get the disease or end of the study , then you can calculate incidence. Incidence is completely different from the prevalence. The former tells you about the risk of disease in a population, while the latter is just a proportion of cases in a population.
According the concept of words Prevalence, Incidence and percentage, we have different explanation for each word.
Prevalence - It is a static study of numbers. For example: You are verifying the number of people which have a car on day X.
Incidence - It is a dynamic study of numbers. For example: You are verifying the number of people which have a car on days X, Y, Z... etc. This number can be variable. It is a study in the time.
Percentage - It is a variable that you can use for calculate a proportion. Can be applied for prevalence and incidence. For example: We have interviewed 10 peoples and only 5 have a car, 50%.
There are areas differents that we can apply It. The basic concept is the same, however, you can apply for different parameters.
The prevalence (P) is the number of cases of disease in a given period.
P=(number of people that have the disease in a given moment)/(number of people in risk of having the disease in the population)*10n
For the prevalence all cases are considered (the new cases and the old cases). It should be a number easy to interpret, so if the frequency of the disease is very high it is possible to multiply by 100, but if it very unusual it is possible to multiply for 100000.
The incidence (I) only considers new cases of disease in a given period, for instance new cases during one year.
I=(number of people that acquired the disease in a given period)/(number of people in risk of having the disease in the population)*10n.
Prevalence and incidence are not related to sample size and do not have to be expressed in percentage. For instance diabetes is a disease with high prevalence and low incidence (once is acquired is permanent), and the influenza have low prevalence but high incidence (very frequent but not long lasting).
Prevalence refers to the number (proportion) of people with a particular disease / condition in a population --
either at a particular point of time (Point Prevalence)
or over a period of time (Period Prevalence).
Incidence refers to the number of new cases arising in a population in a given period of time (like a year).
Prevalence = Incidence * duration of disease.
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