I\'m currently studying Epidemiology. This question is related to person-years i

Question

I'm currently studying Epidemiology. This question is related to person-years in context to number of events of death. It is proposed, that the numbers of person-years can be added together and the number of events such as deaths can be calculated per number of person-years observed. I do not understand the meaning behind this concept. can someone please elaborate.

Let me further elaborate, that I know how to calculate person-years. That is not what I am asking you to explain. However, I don't understant how person-years and the events of death are calculated to find the observed onset of a given disease.

I got this information from the textbook titled: Epidemiology, 5th edition, by Leon Gordis

Explanation / Answer

In the given concept, the incident rate of any disease or death is measured in terms of number of event per person time. For the purpose, person time is calculated by adding the time spent by each individuals in the population under study which is developing the disease. All of the time for each individual at risk is summed up to get the person time. This is done because during the study, the disease development and symptoms occurance varies from person to person depending on health status, age, gender etc. Further, during the study, some individual may enter half way by immigration or new births while others can make exit by death. Also, frequency of the disease development in each individual varies as per their immunity. Some may exit the disease through medication which others have not got due to poor financial status. So the person time is calculated by summing up the time spent by each individual during the study in disease development which in turn gives an average idea of the disease development or death status. And dividing the number of deaths by person time then gives the incident rate of the disease.

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