Blood donations from volunteers serve a crucial role in the nation's health care system. Are Americans any more or less generous about donating blood in some years than others? Are women any more or less willing to give blood than men? To investigate these questions we can analyze data from the General Social Survey, which is a national survey conducted every two years on a nationwide random sample of adult Americans.

1. Did this study make use of random sampling, random assignment, both, or neither? Also explain what your answer means in terms of the scope of conclusions that can be drawn from these data.

2. State the appropriate null and alternative hypotheses, in words and in symbols, to address the research question of whether Americans were more generous with blood donations in one of these years than the other. (Hint: Remember that hypotheses are always about population parameters, and think about whether the alternative should be one- or two-sided before you see the data.)

Data from the 2002 and 2004 surveys are summarized in the following table: 2002 2004 Donated blood in previous 12 months 210 230

Did not donate blood in previous 12 months 1,152 1,106 Total 1,362 1,336

3. For each year, calculate the (conditional) proportion of adult Americans sampled who donated blood in the previous 12 months. Use appropriate symbols to represent them. Also calculate the difference between these sample proportions (taking the 2002 proportion minus the 2004 proportion).

2002 proportion (p2002):

2004 proportion (p2004):

Difference in proportions (p2002 p2004):

4. Produce a segmented bar graph to display the conditional proportions who gave blood in these two years. Comment on what the graph and your calculations from #3 reveal about these two samples