Name: _________________________ Assignment #2 True/False (20 points) 1) _____An association not explained by bias, chance, confounding means an association is causal. 2) ____The connection among intention, decision, behavior, and outcome is not always clear. 3) _____Positive predictive value is more influenced by the sensitivity than the specificity of the screening test. 4) _____Specificity answers the question: “Of all individuals that were free of disease A, what proportion tested negative?” 5) _____Successful treatment programs that shorten the duration of a disease primarily affect the prevalence of the disease rather than the incidence rate. 6) _____The preclinical phase of disease lasts from the biological onset to the development of symptoms. 7) _____Incidence rate is a true rate because the denominator is defined in terms of person-•‐ time whereas cumulative incidence is a proportion. 8) _____A clinical trial entails comparing a group of patients treated with a test treatment to a comparable group of patients receiving a control treatment. 9) _____Experimental study designs have lower validity than cohort studies. 10) _____A “gold standard” is used to determine whether a screening test is effective. Short Answer (30 points) Consider a class with 200 enrolled students. None of the students were ill at the beginning of the school year. On September 30, 10 students reported having gastroenteritis. All continued to be ill on October 1, but all 10 recovered within 3 days. On October 14, 6 more students developed gastroenteritis. All of these students continued to be ill on October 15, but all 6 recovered 5 days later. (Assume that a person cannot get gastroenteritis more than once). 11) Calculate the prevalence of gastroenteritis in the class on October 1. 12) Calculate the prevalence of gastroenteritis in the class on October 30. Name: _________________________ The hypothesis that men in high stress jobs have an increased risk of developing coronary heart disease was tested during an 18-year follow-up study from 1965-1983 of a group of 7,909 men of Japanese ancestry in Hawaii. Of the 7,909 men who completed the first examination at baseline, 4,673 were free of prevalent coronary heart disease (CHD), stroke, and cancer for the duration of the study, while 3,236 had incident CHD. Of the 4,579 men with higher stress jobs, 1,440 of them developed CHD; of the men with lower stress jobs, 1,796 of them developed CHD. 13) What is the study design? Please be as specific as possible. 14) Generate a 2x2 contingency table: 15) Calculate the cumulative incidence of CHD for those exposed to higher stress jobs: 16) Calculate the cumulative incidence of CHD for those unexposed to higher stress jobs: 17) Calculate the relative risk of CHD for the high stress group as compared to the low stress group. 18) Calculate the risk ratio of CHD for the low stress group as compared to the high stress group. 19) Interpret your results for both #17-18 in one sentence: Name: _________________________ Use the following table to answer #20-24: The authors of a study wanted to assess the accuracy of a questionnaire used to diagnose depression. They selected a random set of elderly residents living at an assisted facility and assessed medical records to determine who did and did not have depression, which had been assessed upon arrival at the facility and regularly thereafter. This assessment served as a “gold standard” for the analysis. The table below shows the data from the subgroup analysis. Depression (Questionnaire) No Depression (Questionnaire) TOTAL Results of the depression questionnaire Depression No Depression (Medical record) (Medical record) 52 112 TOTAL 164 8 74 82 60 186 246 20) Calculate the sensitivity of the screening test. 21) Calculate the specificity of the screening test. 22) Calculate the positive predictive value of the screening test. 23) Calculate the negative predictive value of the screening test. 24) If we were to learn that the prevalence of this condition was actually 35%, how would that affect our positive and negative predictive values? a. b. c. d. Despite the change in prevalence, we would expect the PPV and NPV to remain the same Because of the decrease in prevalence, the PPV would decrease and the NPV would increase Because of the increase in prevalence, the PPV would decrease and the NPV would increase Because of the increase in prevalence, the PPV would increase and the NPV would decrease Name: _________________________ 25) Read the article posted on BB entitled “Changes in Physical Fitness and All-Cause Mortality: A Prospective Study of Healthy and Unhealthy Men.” For the following study, identify: a. Study design _______________________________________________________________ b. Exposure variable(s) ________________________________________________________ c. Outcome variables(s) ________________________________________________________ d. Advantage of study design ___________________________________________________
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