BIOS 576A: Biostatistics in Public Health Week 3 Practice with Data

BIOS 576A: Biostatistics in Public Health Week 3 Practice with Data
For each question provide your Stata code, Stata output, and respond to all questions.

1. Body weight (kg) measurements from a group of 11 males with heart disease and 10 males without heart disease are taken at a particular hospital. Assume that the diagnosis of heart disease is made independently of body weight measurement. With the summary statistics for body weight below, use the Stata calculator, and a 0.05 significance level, to test for a significant difference in mean body weight between the diseased and normal groups. Assume that body weight is normally distributed and the variances are equal.

Heart Disease Group

Normal Group

mean

55.61

11.55

56.23

11.54

a) According to the p-value from your results from Stata, do you reject or fail to reject the null hypothesis? Explain why.

b) In a complete sentence, state your conclusions regarding body weight differences in the two groups.

2. Ten patients with advanced kidney complications were treated with the drug captopril over an 8 week period. Urinary protein (g/day) was measured before and after drug therapy, with results in the file PROTEIN. Using Stata, test whether mean urinary protein has changed over the 8-week period. Assume the protein measurement is normally distributed and use a significance level of 0.05. Note: You do not need to generate an additional variable to conduct this test.

a) Based on the resulting p-value do you reject or fail to reject the null hypothesis? Explain why.

b) In a complete sentence, state conclusions regarding differences in proteins over time in this study.

3. Blood levels of lead (variable ld73, in mg/100 ml) were measured in a group of children who lived near a lead smelter in El Paso, Texas, and are found in the file called LEAD.DAT. Forty-six children are in an exposed group (variable Group = 2) and 78 children are in a control group (variable Group = 1). Using Stata, assess if there is a significant difference in the mean lead levels in the exposed and control groups. Assume unequal variances, normality of the lead levels, and use a significance level of 0.05.

a) Based on the resulting confidence interval of the difference in means, do you reject or fail to reject the null hypothesis? Explain why.

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