PRACTICE QUESTIONS FOR FINAL EXAM



PRACTICE QUESTIONS FOR FINAL EXAM

Exam will be based on figures and tables from the journal articles that we have discussed this term.

The following table (from the New England Journal of Medicine, 2007) displays results from a case-control study of oropharyngeal cancer patients. The investigators were looking for associations between HPV and oropharyngeal cancer. Use the table to answer questions 1-5.

[pic]

In Table 3:

a. There is no association between having Positive Oral HPV-16 infection and oropharyngeal cancer because the confidence interval does not cross 1.0.

b. There is a 33.3-fold increase in oropharyngeal cancer in patients seropositive for E6 or E7 but it is not statistically significant.

c. There is a 32.2-fold adjusted increase in the odds of oropharyngeal cancer for those with Seropositive HPV-16 L1 serologic status and it is statistically significant.

d. The data cannot be interpreted because the numbers are too sparse.

e. According to these data, patient who were seropositive for HPV-16 L1 were less likely to develop oropharyngeal cancer.

Calculate the unadjusted risk ratio for the risk of oropharyngeal cancer in patients who were positive for oral HPV-16 infection.

a. 17.6

b. 11.4

c. 3.06

d. 8.0

e. Cannot calculate from the information given

What statistical method was used to calculate the “adjusted odds ratios” given in the table?

a. Linear regression

b. Cox regression

c. Poisson regression

d. Logistic regression

e. Multiple 2x2 tables

The unadjusted odds ratio for HPV-16 L1 seropositivity is 17.6 but the adjusted odds ratio is 32.2. How do you explain this difference?

a. This is most likely an error—as adjustment for confounding should always reduce the magnitude of the odds ratio.

b. The change is irrelevant since both odds ratios are statistically significant anyway.

c. The unadjusted odds ratio was an underestimate—which could happen if some of the confounders were inversely related to exposure or disease.

d. Since both odds ratios are statistically significant, this indicates that there is little confounding going on.

e. The unadjusted odds ratio was artificially inflated due to confounding.

Which of the following represents the correct statistic for comparing oral HPV infection prevalence in cases versus controls?

a. [pic]

b. [pic]

c. [pic]

d. [pic]

e. None of the above; only a non-parametric test should be used here.

The following figure displays the Hazards Ratios derived from five different Cox regression models. Use the table below to answer questions 1-4.

[pic]

1. Which of the following is the result of an unadjusted (univariate) analysis?

a. Female sex.

b. 1.039 (1.012-1.066)

c. 1.023 (0.997-1.049)

d. None of the above. Since this is a Cox-Regression, it is always an adjusted (multivariate) analysis.

2. Weekend admission is a statistically significant predictor of death in all the following except?

a. Model 1 (column 1)

b. Model 2 (column 2)

c. Model 3 (column 3)

d. Model 4 (column 4)

e. Model 5 (column 5)

3. According to the statistical modeling performed by the authors, which of the following variable groups may be explaining the increased risk of death among patients admitted on the weekends for treatment of M.I.?

a. Age of patient and female sex.

b. Mechanical and arrhythmic complications.

c. Longer length of stay when patients are admitted on the weekend.

d. No invasive cardiac procedure within 30 days of admission.

4. Which of the following pair reflects the 1) PRIMARY INDEPENDENT VARIABLE of interest AND the 2) DEPENDENT VARIABLE in this table of Cox Regression Models.

a. Primary Indep: Weekend Admission. Depend Variable: Cardiac Intervention Procedures (including catheterization, PCI, and CABG).

b. Primary Indep: Cardiac Intervention Procedures (including catheterization, PCI, and CABG). Depend Variable: Time to Death.

c. Primary Indep: Weekend Admission. Depend Variable: Time to Death.

d. Primary Indep: Age. Depend Variable: Time to Death.

(We will discuss these statistical techniques on the last day of class, 5/27)

The following figure displays the Kaplan-Meier curves from a randomized trial comparing botulism toxin A with botulism toxin B for the treatment of cervical dystonia (n=122). Patients were followed until their pain returned or until they were censored.

1. Which of the following can be concluded directly from the figure?

a. Botulism toxin A is a better drug for treating cervical dystonia than toxin B.

b. Botulism toxin B is a better drug for treating cervical dystonia than toxin A.

c. The median time to return of pain was longer in the botulism toxin A group than the B group.

d. The median time to return of pain was longer in the botulism toxin B group than the A group.

e. There is a statistically significant difference between the treatments.

2. The authors also ran a univariate Cox regression to get the hazard ratio comparing treatment A to treatment B for the outcome return of pain. The hazard ratio from this model will be:

a. =1.0

b. >1.0

c. ................
................

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