Question: compute the personyears of smoking exposure using the table below...
Question details
 Compute the PersonYears of smoking exposure using the table below. (Hint: add the years at risk of throat cancer (TC) – see examples).
 Once they develop TC they are no longer at risk and their years in the study can’t be counted.
 Add each person’s years of exposure in the right column and enter the value in the box next to “Total PY at Risk of Throat Cancer”.
 Then count the PY at risk for the Current/Former Smokers (exposed) and the PY at risk for the NeverSmokers (not exposed)
 Using the PersonYears for each exposure group as the denominator and the number of TC recorded for each exposure group; compute the Incidence Density for TC risk in current/former smokers (exposed) (ID_{E}) & compute the incidence density for TC risk in never smokers (not exposed) (ID_{NE}).
 The compute the Incidence Density Ratio (also call RR), divide the ID_{E}by the ID_{NE}. This value is interpreted the same as the Relative Risk.
Years in the Study at Risk of Developing Throat Cancer 
Years at Risk 

Person 
Smoker 
1 
2 
3 
4 
5 
6 
7 
8 

A 
Yes 
at risk 
at risk 
TC 
No longer at risk of throat cancer 
2 

B 
No 
at risk 
at risk 
at risk 
at risk 
at risk 
at risk 
at risk 
at risk 
8 
C 
No 

D 
Yes 
TC 

E 
Yes 
TC 

F 
No 

G 
No 
TC 

H 
No 
TC 

I 
Yes 
TC 

J 
Yes 
TC 

Total PY at Risk of Throat Cancer 
 Sum the PersonYears of Exposure for each exposure group? (1 point)
Former/Current Smoker (1/2 point)
Never Smoker(1/2 point)
 How many of the exposed & not exposed participants developed throat cancer (1 point)?
Former/Current Smoker (1/2 point):
Never Smoker(1/2 point):
 What is the Incidence Density for the exposed (ID_{E}) and nonexposed (ID_{NE}) groups? (1 point)
Former/Current Smoker (1/2 point):
Never Smoker (1/2 point):
 Compute the Incidence Density Ratio (IDR). Is the IDR protective or hazardous? (1 point).
10. Using the interpretation for Relative Risk on page 120 of your text, interpret the meaning of the Incidence Density Ratio (1 pt):