College of Public Health and Human Sciences H220: Introduction To Health Data Analysis Spring 2016 Instructor: Harold Bae, PhD, MS (Assistant Professor, Biostatistics) TA: Erin Buth Score: ______ / 20 Due Date: Apr. 14, 2016 Homework 2 1. Data from a study on depression in stroke patients were reported in a paper in the online British Medical Journal (Watkins et al., BMJ 2001; 323: 1159). Respondents were considered to have tested positive if they responded yes to the question \"Do you often feel sad or depressed?\" Respondents with clinical depression (D+) were defined by a more complex measure, the Montgomery Asberg depression rating scale. The study results are shown in the table below. Clinically depressed (D+) T+ (responded yes) 37 T- (responded no) 6 Not clinically depressed (D-) 8 45 A 28 Total Total B 34 a. What are the values for A and B in the table above? (numerical answers) (2 pt) b. What is the probability of having answered yes, given a subject had been diagnosed with clinical depression? (2 pt) c. What is the prevalence of clinical depression in this study of stroke patients? (2pt) d. If the prevalence of clinical depression in the community tested were much lower than it is in this group of stroke patients, which of the following values would change and in which direction? (Highlight the correct answer(s).) (2 pts) 1. Negative predictive value would increase 2. Positive predictive value would decrease 3. Sensitivity would increase 4. Specificity would decrease 2. A study is conducted to assess the association between clinical characteristics and the risk of stroke. The study involves n=1,250 participants who are free of stroke at the study start. Each participant is assessed at study start (baseline) and every year thereafter for five years. The following data were collected in the study relating hypertensive status measured at baseline to incident stroke over 5 years. Free of Stroke at 5 Years Baseline: Not Hypertensive Baseline: Hypertensive Stroke at 5 Years 952 234 46 18 College of Public Health and Human Sciences H220: Introduction To Health Data Analysis Spring 2016 Instructor: Harold Bae, PhD, MS (Assistant Professor, Biostatistics) TA: Erin Buth a. What study design was used in this study? (1 pt) b. Compute the cumulative incidence of stroke in the study. (1 pt) c. Compute the cumulative incidence of stroke in patients classified as hypertensive at baseline. (1 pt) d. Compute the cumulative incidence of stroke in patients free of hypertension at baseline. (1 pt) e. Compute the risk difference of stroke in patients with hypertension as compared to patients free of hypertension. (1 pt) f. Can you compute the incidence rate of stroke given the data above? Justify your answer. (1 pt) 3. Five hundred people are enrolled in a 10-year cohort study. At the start of the study, 50 have diagnosed CVD. Over the course of the study, 40 people who were free of CVD at baseline develop CVD. a. What is the cumulative incidence of CVD over 10 years? (2 pts) b. What is the prevalence of CVD at baseline? (2 pts) c. What is the prevalence of CVD at 10 years? (2 pts)