Cholesterol
and heart attacks
Let’s now calculate the plus four CI for the difference
in percentage middle-aged men who suffer a heart attack
(placebo – drug).
The confidence
interval is (p̃1 − p̃2) ± z*SE
è
(0.0418 − 0.0278) ±
1.645*0.00573 = 0.014 ± 0.0094
We are 90%
confident that the percentage of middle-aged men who suffer a heart attack is 0.46% to 2.34% lower when taking the
cholesterol-lowering drug.
Standard error of the population difference p1 − p2:
4.18%
2030
84
Placebo
2.78%
2051
56
Drug
p̃
n
H. attack
