1. Consider the following study: In 1972, 10,000 male coffee drinkers and 20,000 males who did not drink coffee were examined. The men were then followed for the next 18 years to determine how many developed anxiety during that time period.
700 cases of anxiety were observed, including 200 among the men who did not drink coffee. a) What kind of study is this? b) Construct a 2x2 table for these data:

Coffee Drinker
(exposed)
No Coffee
(unexposed)
Anxiety
(Case)
500
200
No Anxiety
(Non-case)
9500
19800
10000
20000
700 29300 30000 c) Calculate and interpret the appropriate measure of association: d) Calculate the 95% confidence interval for the measure of association in part c) and interpret your findings.

e) After doing the above analysis, a small, but significant fraction of the men were lost to follow up due to change of residence, change of hospitals or doctors, etc. This loss was higher among those who drank coffee and did not have anxiety (15% loss to follow up) than among those that didn’t drink coffee and did not have anxiety (5% loss to follow up).
Construct a 2x2 table for these data:
Calculate the appropriate measure of association:
Did loss to follow up in the study alter the conclusions? If so, what conclusion would you reach now?

1. In 1972, 10,000 male coffee drinkers and 20,000 males who did not drink coffee were examined. The men were then followed for the next
18 years to determine how many developed anxiety during that time period. 700 cases of anxiety were observed, including 200 among the men who did not drink coffee. a) What kind of study is this?
Prospective cohort study
This is a prospective cohort study in which subjects were classified based on exposure (coffee drinking) status at the onset of the study and then followed up over time for occurrence of the outcome (anxiety). b) Construct a 2x2 table for these data:
Anxiety
(Case)
500
No Anxiety
(Non-case)
9500 10000 Coffee Drinker
(exposed)
No Coffee
(unexposed)
200 19800 20000
700 29300 30000

c) Calculate and interpret the appropriate measure of association:
The appropriate measure of association for this cohort study is the relative risk:
RR = [a/(a+b)] / [c/(c+d)] = (500/10000) / (200/20000) =5.00
Among the men participating in this study, the risk of developing anxiety was 5.00 times higher in those who drank coffee compared to those who did not drink coffee during the
18 years of follow up. d) Calculate the 95% confidence interval for the measure of association in part c) and interpret your findings.
Confidence Interval = ( RR ) e

1 .
96 * b a *( a
 b )
 d c *( c
 d )
=
5 .
00 e

1 .
96 *
9500
500 * 10000

19800
200 * 20000
= (4.25,5.88)
This confidence interval does not include the null value of
1.0, therefore coffee consumption is significantly associated with anxiety.

e) After doing the above analysis, a small, but significant fraction of the men were lost to follow up due to change of residence, change of hospitals or doctors, etc. This loss was higher among those who drank coffee and did not have anxiety (15% loss to follow up) than among those that didn’t drink coffee and did not have anxiety (5% loss to follow up).
Construct a 2x2 table for these data:
Anxiety
(Case)
500
No Anxiety
(Non-case)
8075 8575 Coffee Drinker
(exposed)
No Coffee
(unexposed)
200
700
18810
26885
19010
27585
Calculate the appropriate measure of association:
RR = [a/(a+b)] / [c/(c+d)] = (500/8575) / (200/19010) =5.54
Did loss to follow up in the study alter the conclusions? If so, what conclusion would you reach now?
The differential losses to follow up in the two groups did affect our results, which can be seen by comparing the relative risk without loss to follow up (RR = 5.00) with the relative risk after losses to follow up (RR = 5.54). In both instances, however, the conclusion is that men who are coffee drinkers were at higher risk of developing anxiety than men who did not drink coffee.