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

Boy and Girl Infants 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
  1. Is there evidence for a significant statistical change in the proportion of male births in the U.S. over the study period?
  2. 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.]
  3. Provide a plot that illustrates your results.
  4. 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?].