The data set lowbwt.sav contains information for a sample of 100 low birth weight infants born in two teaching hospitals in Boston. Measurements of systolic blood pressure are saved under the variable name sbp and indications of gender-with 1 representing a male and 0 a female-under the name sex.
(a) Obtain a histogram of systolic blood pressure. Based on the graph, do you think that blood pressure is approximately normally distributed?
(b) Use the Shapiro-Wilks test to check for the normality of blood pressure. Carefully state your conclusion.
(c) Obtain the mean and standard deviation of blood pressure by sex. Write a brief summary of these summary statistics.
(d) Test the null hypothesis that among low birth weight infants, the mean systolic blood pressure for boys is equal to the mean for girls. Use a two-sided test at the 5% level of significance. What do you conclude?