Question

Write an explanation to a new staff member in a local health department, one who did not have PHE 502 in her curriculum, of how person-years were obtained for each of the smoking groups. Mention what might be the advantages of using an incidence density versus cumulative incidence in your explanation.

Answer 1

Person years-Person year is a type of measurement take into account to both the number of people in the the study.It is also called survival analysis because the technique was initially developed to look at how various factors affected the length of life.

Person year were obtained for each of the smoking groups. Using exact method in this method we use administrative type of data that contains birth date, date of event. We can use exact date to calculate person year if the exact dates of birth, entry into and/or exit from the study are unknown, these must be approximated.If a person enters and leaves a study during the same year, s/he has contributed 0.25 year.

Let us consider a hypothetical example for smokers in age group

Person	Age Group	Age at Start	Age at end	Person Years=(Age at end-Age at start)
1	20-25	24.504	25	0.496
1	25-30	25	30	5.00
1	30-35	30	35	5.00
1	35-40	35	37.501	2.501
2	40-45	66.503	70	3.497
2	45-50	70	71.970	1.970

Incidence is a measure of the occurrence of new cases of disease during a span of time.

While is cumulative incidence generally used in situations where the follow-up time is relatively short and there is relatively little loss to follow-up but this problem couldn't occur in incidence rate.

If subjects don't die for another reason, it is difficult to follow people for long periods of time, and subjects can become lost to follow-up , which also means that their outcome status is unknown

The amount of life expectancy lost for each pack of cigarettes(10 cigarettes) smoked is 28 minutes and the year of life expectancy a typical smoker loses is 25 years.