## Homework 2

Due Wednesday, 16 October 1996

- For this problem, use the data set estriol.dat
(in the Other
Data Sets folder).

Greene and Touchstone (1963) studied the relationship between birthweight
and measured hormone levels in pregnant women near the end of their term.
The data set contains three variables: a patient identification number,
a measurement of estriol production over a 24-hour period (mg/24 hr), and
the weight (in 100 gm units) of the baby at birth.

(a) Construct a scatterplot of birthweight and estriol. (Use `graph`
or `plot` commands to do this in Stata.)

(b) Calculate the estimated regression of birthweight on
estriol.

(c) On average, by how much does birthweight increase for each additional
mg of estriol produced by the mother?

(d) What would the predicted birthweight be for a child whose mother
had an estriol level of 19 mg/24 hr?

(e) A colleague asks you to predict what the birthweight would be corresponding
to an estriol reading of 35. What would you say?

- For this problem, use the data of Selvin, Table 1-4. (This data set
can be accessed from the Selvin
Data Sets button on the home page for Stat 227.)

Do boys and girls born to women over 40 differ in birthweight? Use (a) a
t-test, (b) an analysis of variance test, and (c) a regression model to
address this question. Assuming that `bwt` and `sex` refer
respectively to the birthweight and infant-sex variables in the data set,
the following Stata commands may be helpful:

` ttest bwt, by(sex)`

oneway bwt sex, tabulate

regress bwt sex

Comment on the information provided by each of the approaches, and
on the extent to which the conclusions drawn from the three approaches
are similar to or different from one another.

- Selvin, problem 5, page 64.

- For this problem, use the data of Selvin, Table 1-4.

Are there individual variables in the tabulated data that do a better job
of predicting birthweight than maternal weight gain (the variable that was
discussed in class)? If so, which one(s) and how much better are they? If
not, how much better is weight gain than anything else?

*Last updated 8-Oct-96*

For questions, send mail to r-thisted@uchicago.edu
or mcpeek@galton.uchicago.edu