Question 1

Assume the estimated odds ratio of obesity for the amount of weekly exercise (in minutes) is 0.93 (95% CI: 0.88, 0.99). Interpret this odds ratio for every minute and for 30-minute increases in exercising time.

Accepted Answer

For every minute increase in exercising time, the odds ratio of obesity is decreased by 7%.
To obtain the odds ratio for every 30 minutes, we need to find the beta estimate first. Since exp(b) =0.93, b = ln(0.93). exp(30*ln(0.93)) = 0.11. Thus, for every 30 minutes increase in exercising time, the odds of obesity is decreased by (1-0.11)*100% = 89%. Since the confidence interval does not contain 1, the true odds ratio is not 1.

Question 2

In the following scenarios, p = the probability of lung cancer. If the odds ratio estimate is 1.2, interpret for the following variables: 
a.age (continuous) 
b.education level (graduate school vs. high school) 
c.race (Black vs. White) 
d.smoking status (smoker vs. nonsmoker)

Accepted Answer

a.The odds ratio of lung cancer is increased by 20% for every unit of increase in age.
b.The odds of lung cancer for people with graduate school degree is 1.2 times that of people with high school degree.
c.The odds of lung cancer for Black is 1.2 times that of White.
d.The odds of lung cancer for smokers is 1.2 times that of nonsmokers.

Question 3

Which of the following is NOT an advantage of a pie chart?

Accepted Answer

A)   relate parts to whole
B)   represent a good alternative when numerical summaries are harder to present
C)   investigate the shape of the distribution
D)   allow easy interpretation and understanding C

Question 4

Briefly describe the similarity and difference between odds and risks. At what value of odds and risks will the probability of success be larger than the probability of failure?

Accepted Answer

The answer of Briefly describe the similarity and difference between...

Question 5

Choose the most appropriate graphical presentation (pie chart or bar graph) for the following examples. Provide a rationale for your choice.
a.To show the composition of racial distribution of a certain disease. 
b.To compare the proportion of smoking between males and females. 
c.To show an association between weight perception and age groups. 
d.To compare the number of cases of flu in each month

Accepted Answer

The answer of Choose the most appropriate graphical presentation (pie...

Question 6

Describe how confidence intervals are used to determine whether an odds ratio is different than 1?

Accepted Answer

The answer of Describe how confidence intervals are used to...

Question 7

Briefly explain how the expected and observed cell counts are obtained. How do they influence the significance of the hypothesis test?

Accepted Answer

The answer of Briefly explain how the expected and observed...

Question 8

Why is it inappropriate to estimate risks directly in a case-control (retrospective) study?

Accepted Answer

The answer of Why is it inappropriate to estimate risks...

Question 9

When is it appropriate to interpret odds ratio as relative risk?

Accepted Answer

The answer of When is it appropriate to interpret odds...

Question 10

Briefly describe the difference between a case-control study and a cohort study in terms of the way data are collected. What measure of association is appropriate in each study?

Accepted Answer

The answer of Briefly describe the difference between a case-control...

Question 11

The chi-square test of independence is used to assess which of the following hypotheses?

Accepted Answer

A)   Whether the samples are independently distributed.
B)   Whether the samples are associated with each other.
C)   Whether the variables are independently distributed.
D)   Whether the variables are associated with each other.

Question 12

Suppose an odds ratio between gender (male, female) and smoking status (yes, no) is 2.5. Explain why it is incorrect to interpret the odds ratio as "the probability of smoking for males is 2.5 times that for females." Provide a correct interpretation.

Accepted Answer

The answer of Suppose an odds ratio between gender (male,...

Question 13

The confidence interval width decreases as which of the following increases?

Accepted Answer

A)   level of confidence
B)   estimated variance of the proportion
C)   sample size
D)   size of the null parameter

Question 14

Specify an appropriate test (nonzero correlation test, row mean scores differ test, and general association test) for the following types of categorical variables. Justify the choice.
a.education level versus social class (upper, middle, lower)
b.gender versus anxiety rating (none, moderate, severe) 
c.race versus political affiliation

Accepted Answer

The answer of Specify an appropriate test (nonzero correlation test,...

Question 15

What is the denominator(s) used to calculate the percentages of the first cell.

Accepted Answer

The answer of What is the denominator(s) used to calculate...

Question 16

Can a variable be regarded as both ordinal and dichotomous? Why or why not?

Accepted Answer

The answer of Can a variable be regarded as both...

Question 17

Which of the following is NOT required to determine the sample size for a test of two proportions?

Accepted Answer

A)   power
B)   significance level
C)   proportion estimates
D)   standard deviation

Question 18

For the first cell in the following contingency table, interpret the frequency, percent, row percent, and column percent.

Accepted Answer

The answer of For the first cell in the following...

Question 19

Identify the following variables as nominal, ordinal, or dichotomous. Provide a justification for your choice.
a.Types of diabetes: type 1 (insulin-dependent), type 2 (non-insulin-dependent), gestational diabetes mellitus. 
b.Time to recurrence: 0-2 years, 2-4 years, more than 4 years. 
c.Clinic sites: Lexington, Covington, Frankfort, Nashville, Bowling Green. 
d.Smoking status: smoker, nonsmoker. 
e.Levels of body mass index (BMI): normal, overweight, obese. Types of vaccine administration: oral, injection, puncture. 
f.Types of residency: urban, rural.

Accepted Answer

The answer of Identify the following variables as nominal, ordinal,...

Question 20

Which of the following is NOT a good descriptive statistic for categorical variables?

Accepted Answer

A)   proportions
B)   percentages
C)   counts
D)   means

Exam 4: Categorical Data: Comparisons and Associations