Part 2: Two by Two Tables and Measures of Association (42 total points)

Problem 1: Risk Factors for Heart Disease and Ethnicity (9 points)

Below are some of the data from a cross-sectional study of risk factors for heart disease among Mexican American and Non-Hispanic White women hospitalized for heart attacks in San Antonio, Texas.

1. Assuming that Non-Hispanic Whites are the exposed group, and Mexican Americans are the unexposed (called the referent group) calculate all six prevalence ratios (one for each risk factor) and list the answers in the table. do not show all steps. Round to two places after the decimal. (3 points)
2. Precisely interpret each prevalence ratio in one sentence each below the table (3 points)
3. Which prevalence ratios are protective and which ones indicate a possible risk factor for Non-Hispanic Whites relative to Mexican Americans? Which indicates no appreciable difference? (3 points)

Table 1: Prevalence of Risk Factors for Heart Disease in a Sample of Mexican American and Non-Hispanic White Women in San Antonio, Texas

	Mexican Americans		Non-Hispanic Whites
	Prevalence (%)		Prevalence (%)	Prevalence Ratio
Previous MI	20.3		31.1
Diabetes	53.0		34.1
Hypertension	89.6		38.9
High Cholesterol	35.7		32.7
Current Smoker	24.7		42.7
Ever Smoked	53.1		66.4

Problem 2: Neural Tube Defects and Vitamin Use (10 points)

An investigator wanted to determine whether vitamin deficiency was associated with birth defects.By reviewing the birth certificates during a single year in a large U.S. county, the researcher located 189 infants born with neural tube defects (a birth defect of the spinal cord or brain).A total of 600 other births were selected at random from the certificates. Mothers were given a questionnaire regarding their diets during the pregnancies. Among mothers who gave birth to an infant with a neural tube defect (NTD), 84 reported no use of supplementary vitamins. A total of 137 control mothers did not use a vitamin supplement. The data are presented in the two by two table shown below.

Table 2:2 by 2 Table of Study of Neural Tube Defects and Vitamin Use

	NTD	Other Births	Total
Supplementary Vitamin Use	105	463	568
No Supplementary Vitamin Use	84	137	221
Total	189	600	789

1. What is the outcome being studied here? (1 point)
2. What is the exposure? (1 point)
3. What is the study design? (2 points)
4. Calculate the most appropriate measure of association (odds ratio, prevalence ratio or relative risk) given the study design. Name the type of ratio you are calculating. Show all steps, including numerators and denominators, as well as the final answer, rounded to two places after the decimal. (3 points)
5. Interpret this ratio. Please note that format differs for prevalence ratios, odds ratios and relative risks. (2 points)
6. Does this measure of association (PR, OR, or RR) represent a positive (possible risk factor) or negative (possible protective factor) association? (1 point)