STAT 405 Fall 2014 - Homework 7 (32 pts.)
Due Wednesday, October 28th
1) Risk of Bacteriuria Among OC Users and Nonusers
The presence of bacteria in the urine (bacteriuria) has been associated with kidney
disease. Conflicting results have been reported from several studies concerning the
possible role of oral contraceptives (OCs) in bacteriuria. The following data were
collected in a population-based study of non-pregnant premenopausal women
younger than age 50.
Overall Table
a) Estimate the crude OR for Bacteriuria (bacteria in the urine) associated with OC use
from the overall table. Also estimate the OR for bacteriuria associated with OC use for
each age group using the stratified tables. Does age group appear to be a confounding
factor? Discuss. (6 pts.)
b) Perform a significance test to examine the association between OC use and bacteriuria
after controlling for age. Summarize your findings. (4 pts.)
c) Estimate the OR in favor of bacteriuria for OC users vs. non-OC users after controlling
for age. How does this compare to the crude OR calculated in part (a)? (3 pts.)
d) Is the association between bacteriuria and OC use comparable among the different age
groups? Conduct an appropriate test. Summarize your findings. (4 pts. BONUS)
2) Fracture Incidence Between Raloxifene and Placebo Treated Women
A study of raloxifene and incidence of fractures was conducted among women with evidence of
osteoporosis. The women were initially divided into two groups: those with and those without
pre-existing fractures. The women were randomized to raloxifene or placebo and followed for 3
years to determine the incidence of new vertebral fractures, with the results shown in the tables
below.
No Pre-existing Fractures
Treatment
Raloxifene
Placebo
Column
Totals
New fractures
No new fractures
34
68
1466
1432
Row
Totals
1500
1500
102
2898
3000
New fractures
No new fractures
103
170
597
630
Row
Totals
700
800
273
1227
1500
Pre-existing Fractures
Treatment
Raloxifene
Placebo
Column
Totals
a) Among those with pre-existing fractures, test whether raloxifene affects the incidence of
new fractures. Estimate the OR (with a 95% CI) for a new fracture associated with
raloxifene vs. placebo. Discuss these results. (6 pts.)
b) Repeat (a) for those without pre-existing fractures. (6 pts.)
c) Does the presence of pre-existing fractures appear to be a confounding factor? Explain.
(3 pts.)
d) Conduct an appropriate test for determining whether an association between raloxifene
treatment and new fractures is present controlling for pre-existing fracture status.
Summarize your results. (4 pts.)