Practical assignment 4
5 points (5% of the grade)
You conduct a prospective cohort study to see if watching television is associated with colorectal cancer. You divide the exposed group into three categories: those who watch <1 hour per day (low), those who watch 1-4 hours a day (moderate), and those who watch >4 hours a day (high). You follow the participants for five years. Of the 5000 participants who did not watch TV, 25 participants developed colorectal cancer. Of the 2000 with low TV exposure, 10 people developed colorectal cancer. You observed 15 cases of cancer among the 2000 participants with moderate TV exposure. Finally, 10 people developed colorectal cancer among the 1000 participants with high TV exposure. (0.8 points)
Calculate the cumulative incidence of colorectal cancer (per 1000) FOR EACH of the four groups, separately: no TV, low, moderate and high exposure. (0.4 points)
Calculate the cumulative incidence ratio FOR EACH of the three TV-watching groups compared to those who did not watch TV. (0.4 points)
The authors of a study looking at the effect of alcohol intake on colorectal cancer reported an incidence rate ratio of 2.1 (95% CI: 2.05-2.31) when comparing heavy drinkers to light or nondrinkers. The authors of a second study examining the effect of green tea consumption on colorectal cancer reported an incidence rate ratio of 0.85 (95% CI 0.56-1.75) when comparing green tea drinkers to nondrinkers. How do you interpret the findings of both studies? Discuss the
i) direction,
ii) strength and
iii) statistical significance for BOTH associations (0.8 points)
Your colleague conducted a study to examine the rate of coronary heart disease in the capital cities of the world relating to the average income. Results showed that, within the cities studied, coronary heart disease is higher in the richer cities than in the poorer ones.
Your colleague concludes that being rich increases your risk of heart disease. What is the problem with drawing such a conclusion from this type of study? How this problem is called? (0.4 points)
Pap smear screening is currently the accepted method for early detection of cervical cancer and women with abnormal Pap smear result are referred for a colposcopy for definitive diagnosis. To see whether repeat Pap screening would reduce the number of unnecessary referrals, 110 women with abnormal Pap (to the first Pap smear) were given both a second Pap smear and colposcopy. The colposcopy showed that 13 women had high-grade lesions and 97 did not. The result of the second Pap smear was abnormal for 12 of the women with high-grade lesions and abnormal for 72 without high-grade lesions. (1.2 points)
Create the 2×2 table. (0.4 points)
Calculate and interpret the sensitivity of this screening test. (0.4 points)
Calculate and interpret the specificity of this screening test. (0.4 points)
Public health stakeholders decide to target their diabetes-screening program to higher risk populations (e.g. overweight, family history, etc.). Prevalence of undetected diabetes in this higher risk population is approximately 8.5%. 10,000 persons total were screened during the program. The sensitivity and specificity associated with this screening test are 22.9% and 99.8 %, respectively. (1.2 points)
Create the 2×2 table (0.4 points)
If someone tests positive, what is the chance that this person actually has diabetes? (0.4 points)
If someone tests negative, what is the chance that this person does not have diabetes? (0.4 points)
Name three approaches for prevention (primary, secondary and tertiary) for each of the following health problems/conditions. (0.6 points)
Diabetes type II (0.3 points)
Mortality and morbidity due to gun violence (0.3 points)
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