**Note**Your answers to the questions below should follow the expectations for homework found here. Due date is on the Dates page.

## Male-Female Birth Ratio

Davis *et al.* (1998) observed a decline in the ratio of male to female births in several industrialized countries and explored whether that result was an indicator of larger health issues. The data below are the proportion of male births (PropMale) for the United States. Use these data to answer the questions further below. [*Note: The data are wrapped onto multiple lines simply to save space. Carefully check that your data entry is correct.*]

Year: 1970 1971 1972 1973 1974 1975 1976 PropMale: 0.5134 0.5126 0.5125 0.5128 0.5133 0.5132 0.5128 Year: 1977 1978 1979 1980 1981 1982 1983 PropMale: 0.5128 0.5129 0.5127 0.5129 0.5126 0.5123 0.5127 Year: 1984 1985 1986 1987 1988 1989 1990 PropMale: 0.5122 0.5126 0.5122 0.5120 0.5121 0.5120 0.5120

- Is there evidence for a significant statistical change in the proportion of male births in the U.S. over the study period?
- At what average annual rate (i.e., how much per year) did the proportion of male births change? [
*Be specific about the direction of change.*] - Provide a plot that illustrates your results.
- Explain why the p-value for the slope is so small even though the value of the estimated slope is such a small number [i.e., how is it possible that such a small value for the slope can be considered to be different from zero?].