Appendix B: Answers to Exercises

APPENDIX B: ANSWERS TO EXERCISES

CHAPTER 2

1. This is a retrospective cohort or case–control study because the study leverages data from an historical data source and includes both case and control groups.

2. This is an observational longitudinal study that is best categorized as a cohort study. The cohort here is newly diagnosed cancer patients.

3. This study design is interesting, and some might be tempted to call it case–control. The purpose was to compare self-reported therapy with actual therapy. Both of these measures (self-reported and actual) occurred at the same time, so the study also has some characteristics of a cross-sectional study. Our opinion is that the study is case–control, but it illustrates the difficulty in classifying studies cleanly into any scheme.

4. The study is observational and is a matched case–control study.

5. The study is a placebo-controlled randomized clinical trial.

6. The group of subjects was identified and initial data collection occurred in 1976; the same subjects were followed up in future years. The study design is, therefore, best described as a cohort or prospective study to identify risk factors.

7. Several study designs are possible, but the most realistic is an observational study. A case–control study provides information faster, but several case–control studies are required; a group of cases for each cause of death and type of cardiovascular morbidity needs to be identified. We suggest you use one of the electronic search programs to see if you can locate a copy of a cohort study, and, if so, read and discuss the pros and cons of how the study was done.

CHAPTER 3

1. The sum of the deviations (22.26, 3.36, 15.46, 6.96, … −7.84, −17.04, −0.14) is zero.

2. 1. Using the Numerical Summary in R Commander or the Descriptives program in SPSS, the mean SF-12 Total Score for the 1,132 subjects was 58.0 with a standard deviation of 24.8.

   2. See Table B–1.

   3. See Figure B–1.

3. Table Graphic Jump Location

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   SF12_total_score
   age_cat	N	Mean	Median	Std. Deviation	Minimum	Maximum
   ≤60	223	61.31	67.08	24.82	5.42	97.92
   61–70	366	62.76	67.29	24.25	3.33	100.00
   71–80	358	56.09	55.21	24.58	5.00	100.00
   >80	182	47.89	42.82	22.95	3.75	94.17
   Total	1129	57.96	59.17	24.79	3.33	100.00

   Age was available for 1,129 patients. The mean age must be estimated using the weighted means formula. It is found by multiplying the midpoint of each age interval by the count:

   $[(223×55.5)+(366×65.5)+(358×75.5)+(182×85.5)]/1129=69.92$

   The mean SF-12 Total Score is estimated by multiplying the count by the mean in each age group:

   $[(223×61.31)+(366×62.76)+(358×56.09)+(182×47...$