Part I True-False Statements: Fill in T or F (4 points each)
1. In a regression involving age and serum cholesterol level, the “least squares” or “best fit” line calculated from the sample data estimates the age-adjusted mean serum cholesterol level in the population. ___
2. If in a random sample of data we find the linear correlation coefficient, r, to be highly significant (p < 0.001), we may conclude that there is a dependent relationship between Y and X in the population. ___ 3. The following data are from a case-control study investigating a possible relationship between radiation exposure and myeloid leukemia: Case Control Exposed 11 8 Unexposed 4 15 The appropriate procedure for evaluating the significance of such data is the Fisher exact test. ___ 4. The maximum likelihood method is used to estimate parameters in logistic regression? ___ 5. In a logistic regression model with 2 predictor variables (risk factors A and B) and no interaction term, the estimated relative risk (RR) for subjects exposed to both risk factor A (adjusted RR estimate=2.0) and risk factor B (adjusted RR estimate=1.5) is 3.5. ___ Part II Brief Responses (4 points each) 1. Part 1: For a fixed sample size: as the number of independent variables in a regression model increases, the power of the regression ___ a) increases b) decreases Part 2: When a potential confounding variable is found to affect the β-coefficient estimate for the variable of interest in a regression model and is therefore added to the model, the coefficient of determination (R2) ___ a) increases c) decreases 2. An F-test for _________________ must be performed prior to conducting an analysis of covariance (ANCOVA). 3. Part 1: Under what circumstances are chi-square tests biased? ___ a) if any expected value is less than 1.0 or> 25% of the expected values are less than 5.0
b) small sample size
c) when there is 1 degree of freedom
d) all of the above
Part 2: What is the best statistical test to apply when dealing with simple follow-up data (single 2 x 2 table)? ___
a) chi-square test
b) fisher exact test
c) binomial test
4. Refer to the figure below:
Part 1: What is the estimated mean SBP for age 30? ___
Part 2: What is the estimated mean SBP for age 80? ___
5. As health commissioner of city B you have decided to implement a $10 million exercise program if results from a recently concluded cohort study in 2,000 males aged 40-59 years showed there was 95% confidence (exact binomial) that the relative risk (RR) among subjects with a baseline resting heart rate (HR) > 80 beats/min vs. those with a baseline resting HR ≤ 80 beats/min was different from 1.50. The RR estimate was 1.55 with a 95% confidence interval of 1.31 to 1.91. What is your decision? ___
a) Implement the program.
b) Do not implement the program.
6. Part 1: Name one limitation when using the Mantel-Haenszel method to control for confounding in case-control studies.
Part 2: Name one limitation when using matching to control for confounding in a case-control study?
7. Name 2 types of censoring that can occur during follow-up in a cohort study or clinical trial.
8. A potential confounding variable should be included in a multiple proportional hazards regression model if ___
a) it is an independent risk factor for the outcome
b) it is a statistically significant predictor for the outcome
c) it differs in frequency between exposed and unexposed study subjects
d) choices a and c
e) choices a and b
f) all of the above
9. Using a box or arrow diagram, show how the total sum of squares is partitioned in a 1-way repeated-measures ANOVA?
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