What are the appropriate time to estimate the incidence for any medical problem and how can differentiate from prevalence to be more reliable and realistic number figures?
The incidence of a disease is the number of new patients over a period of time.The incidence rate is calculated by relating this number of new patients ( incident population) to the size of the population target,always during a given period period.This rate is one of the most important criteria for assessing the frequency and speed of occurrence of new cases with a pathology.The prevalence is the proportion of the population affected by the disease at any given time.
Please note that the incidence is usually (but not necessarily) calculated for acute communicable diseases, and the prevalence usually calculated for the chronic non-communicable disease. You have asked about the best time to calculate the incidence: of course it should be at the end of the period. eg incidence of COVID-19 during the year 2021, it is the number of cases of COVID-19 developed during 2021 (numerator) among people who were free from COVID-19 at Jan 1, 2021 (denominator). If you calculate the point prevalence of COVID-19 now, it would be very low, but if you calculate the period prevalence (eg during the previous year) it would be high.