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Week 8: Data Interpretation and Confounding Exercise

Exercise on data interpretation and confounding variables.

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    1 Week 8: Data Interpretation and Confounding Exercise Table 1 below describes data from a prospective cohort study examining the association between type of work schedule and the risk of prostate cancer in men. Table 1: Incidence of prostate cancer in 14,052 male workers according to type of work schedule Work schedule Daytime Fixed night Rotating shift No. of subjects with no diagnosis of prostate cancer at the time of enrollment in the study 11,269 982 1,801 No. of person - years of follow - up 89,179 8,272 14,523 No. of new prostate cancer cases 21 3 7 Express your answers as per 10,000 person - years of follow - up where appropriate. A. What is the incidence density of prostate cancer in all participants in the study? (2 points) Shift the rows and columns of the above table and calculated the required ratios. The incidence density of prostate cancer in all participants in the study is in the below table . Work schedule No. of subjects with no diagnosis of prostate cancer at the time of enrollment in the study Incidence density No. of person - years of follow - up Incidence density No. of new prostate cancer cases Incidence density Total Day time 11,269 0.112 89,179 0.888 21 0.00021 100,469 Fixed night 982 0.106 8,272 0.894 3 0.00032 9,257 Rotating shift 1,801 0.110 14,523 0.889 7 0.00043 16,331 B. What is the incidence density of prostate cancer in daytime workers? (2 points) The incidence density of prostate can cer in day time workers is 0.00021

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    2 C. What is the incidence density of prostate cancer in fixed night workers? (2 points) The incidence density of prostate cancer in fixed night workers is 0.0 0032 D. What is the incidence density of prostate cancer in rotating shift workers? (2 points) The incidence density of prostate cancer in rotating shift workers is 0. 00043 E. What is the ratio of the person - time incidence (or incidence density) of prostate cancer in fixed night shift to the person - time incidence of prostate cancer in Daytime workers? (2 points) The ratio of the person - time incidence (or incidence density) of prostate cancer in fixed night shift to the person - time incidence of prostate cancer in Daytime workers is = 0.894 / 0.888 =1.007 F. What is the ratio of the person - time incidence of prostate cancer in rotating shift to the person - time incidence of prostate cancer in Daytime workers? (2 points) The ratio of the person - time incidence of prostate cancer in rotating shift to the person - time incidence of prostate cancer in Daytime workers is = 0.889 / 0.888 = 1.001 G. How do rates of prostate cancer among fixed night and rotating shift compare to the rate of prostate cancer in daytime shift? What would you conclude about the relationship between work schedule and risk or rate of prostate cancer? Why? (2 points) Rate of prostate cancer among fixed night compared to rate of prostate cancer in daytime shift is =0.00032/0.00021 =1.55 This means prostate cancer among the people who working in fixed night is 1.55 times more compared to the people who are working in day shift. Rate of prostate cancer among rotating shift compared to rate of prostate cancer in daytime shift is =0.00043/0.00021 = 2.05 The prostate cancer among the people who are working in rotating shift is 2.05 times more than the people who are working in day shift. From the above ratios, risk of prostate cancer is low for the people who are working in dayshift. Which means, the risk of prostate cancer for the people who are working in night shift/rotating shift is more than the people who are working in day shift. Next, the risk of prostate cancer in rotating shift people is more than the people who are working in the night shift.

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