STA 3024
Assignment 3: Key for Form 3 7
1. (8 points=2pts for each answer)
•
X
2
≈
15
.
5589
•
expected cell count:
Treatment
fatalattack
nonfatal
noattack
Placebo
10.98
119.77
10929.25
Aspirin
11.02
120.23
10970.15
•
pvalue
≈
.
000418
•
decision: we reject the hypothesis of independence of Myocardial infarction and Aspirin.
2. (8 points=4 for table and 2 for each interpretation)
Standardized residuals:
Treatment
fatalattack
nonfatal
noattack
Placebo
.295
2.76
.280
Aspirin
.294
2.76
.28
Interpretation: The residuals in the first and the last cells of the first row are lower in absolute
value than 2.Thus:
there is not enough evidence that the population number of subjects taking placebo and having
fatal heart attack is any different than the number we would expect if the treatment were
independent of the Myocardial infarction.
Similarly there is not enough evidence that the
population number of subjects taking a placebo and having no attack is any different than the
number we would expect if Myocardial infarction was independent of Treatment.
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 Spring '08
 TA
 Statistics, cell phone, 2pts, 1pt

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