Measures of Association

The problem includes several different scenarios in which you will calculate several measures of association (prevalence ratio, relative risk) and attributable risk.

The table below is the general 2 x 2 table for epidemiologic studies.

Exposure	Outcome
Yes	No	Total
Yes	a	b	a + b
No	c	d	c + d
	a + c	b + d	a + b + c + d = T or N

1. A cross-sectional study was conducted among high school adolescents who participated in the New Mexico Youth Risk Behavior Survey in 2017 to examine the effect of sexual identify (exposure) on seriously considering attempting suicide in the past year (outcome). Of the 5,274 total respondents, 644 were gay, lesbian or bisexual (exposed category), and of these, 257 reported seriously considering suicide. Of the 4,630 who reported they were straight (unexposed category), 650 reported seriously considering suicide.

a. Complete the table below using the data in the paragraph and specific labels.

Exposure	Outcome
		Prevalence %

b. Calculate the prevalence ratio comparing prevalence of considering suicide in gay/lesbian/bisexual adolescents (exposed) to straight adolescents (unexposed).

c. Summarize the prevalence ratio in a sentence.

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2. A Canadian study in May 2020 surveyed 618 parents with children <18 years currently living at home. It compared changes in mental health (outcome) since the onset of the pandemic in parents who were unemployed (exposed, N=86) to those who were employed (unexposed, N=532). In the unemployed parent group, 44 reported that their mental health had deteriorated; in the employed parent group, 230 reported that their mental health had deteriorated.

a. Complete the table below using the data in the paragraph and specific labels.

Exposure	Outcome
		Prevalence (%)

b. What is the prevalence of deteriorated mental health in the two groups of parents, unemployed and employed? Complete the table with your calculations.

c. What is the prevalence ratio of deteriorated mental health comparing unemployed to employed parents? Summarize this in one sentence.

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3. A study examined the association between exposure to magnetic fields such as those coming from high tension power lines and the risk of leukemia. Study participants were classified as having low, medium and high exposure.Since there was no true "unexposed" group, use the low exposure group as the baseline when you calculate the relative risk.

a. Complete the table by calculating the cumulative incidence for the three exposure levels.

Magnetic Field Exposure	No of Leukemia Cases	Total Participants	Cumulative Incidence	Relative Risk
High	30	674
Medium	61	1,469
Low	2,264	67,424

b. Using the low exposure group as the baseline, calculate the relative risks for the other two exposure levels.

c. Summarize the relative risk in one sentence for the medium exposure group compared to low exposure group.

d. Summarize the relative risk in one sentence for the high exposure group compared to the low exposure group.

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4. Let us go back to the British Doctors Study. Doll and Hill completed a ten-year follow-up study in 1961. Now, let us use some of our measures of association to further analyze the information presented in this newer paper. We will focus on male doctors smoking cigarettes compared to those not smoking any type of tobacco. The outcome will be lung cancer. The information from the 1961 study is summarized in the table below.

Smoking Status	Lung Cancer Death Rate per 1,000 P-yrs.	Relative Risk	Attributable Risk	Attributable Risk Percent
Cigarette smoker	0.96
Non-smoker	0.07	xxx	xxx	xxx

a. Complete the table by calculating the relative risk, attributable risk, and attributable risk percent.

b. Summarize your result for the relative risk in one sentence.

c. In one sentence, summarize the attributable risk for cigarette smokers.

d. In one sentence, state the percent of lung cancer cases that could be prevented if smokers did not smoke.