Epidemiology Measures of Effect

MEASURES OF EFFECT

Calculate and interpret measures of effect in different epidemiologic study designs.

A. A cohort study is conducted to assess the association between clinical characteristics and the risk of stroke. The study involves n=1250 participants who are free of stroke at the study start (baseline). The data in Table 4 below shows hypertensive status measured at baseline and incident stroke at five years.

Table 4. Hypertension status at baseline and stroke five years later
	Stroke at 5 years
Hypertension at baseline	Yes (+)	No (-)
Yes (+)	18	234
No (-)	46	952

Compute the prevalence of hypertension among study participants at baseline. Interpret.

Compute the cumulative incidence of stroke in this study. Interpret.

Compute the cumulative incidence of stroke in patients classified as hypertensive at baseline. Interpret.

Compute the risk difference of stroke in patients with hypertension as compared to patients free of hypertension. Interpret.

Compute the relative risk of stroke in patients with hypertension as compared to patients free of hypertension. Interpret.

B. A case control study is conducted to assess the relationship between heavy alcohol use during the first trimester of pregnancy and miscarriage. Fifty women who suffered miscarriage are enrolled along with 50 who delivered full-term. Each participant’s use of alcohol during pregnancy is ascertained. Heavy drinking is defined as four or more drinks on one occasion. The data are shown in Table 5.

Table 5. Alcohol use and outcome during pregnancy
	Miscarriage
Heavy alcohol use	Yes (+)	No (-)
Yes (+)	14	4
No (-)	36	46

Compute the odds of miscarriage in women with heavy alcohol use during pregnancy. Interpret.

Compute the odds of miscarriage in women with no heavy alcohol use during pregnancy. Interpret.

Compute the odds ratio of women with heavy alcohol use compared to women with no heavy alcohol use during pregnancy. Interpret.

phc6000_lecture5_measures_assoc

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