Question

• Compute the Person-Years of smoking exposure using the tablebelow. (Hint: add the years at risk of throat cancer (TC) – seeexamples).
• Once they develop TC they are no longer at risk and their yearsin the study can’t be counted.
• Add each person’s years of exposure in the right column andenter the value in the box next to “Total P-Y at Risk of ThroatCancer”.
• Then count the P-Y at risk for the Current/Former Smokers(exposed) and the P-Y at risk for the Never-Smokers (notexposed)
• Using the Person-Years for each exposure group as thedenominator 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 forTC risk in never smokers (not exposed) (ID_NE).
• The compute the Incidence Density Ratio (also call RR), dividethe ID_Eby the ID_NE. This value is interpretedthe same as the Relative Risk.

		Years in the Study at Risk of Developing ThroatCancer								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 P-Y at Risk of Throat Cancer

1. Sum the Person-Years of Exposure for each exposure group? (1point)

Former/Current Smoker (1/2 point)

Never Smoker(1/2 point)

2. How many of the exposed & not exposed participantsdeveloped throat cancer (1 point)?

Former/Current Smoker (1/2point):

Never Smoker(1/2point):

3. What is the Incidence Density for the exposed (ID_E)and non-exposed (ID_NE) groups? (1 point)

Former/Current Smoker (1/2point):

Never Smoker (1/2 point):

4. Compute the Incidence Density Ratio (IDR). Is the IDRprotective or hazardous? (1 point).

10. Using the interpretation for Relative Risk onpage 120 of your text, interpret the meaning of the IncidenceDensity Ratio (1 pt):