Studies have concluded that smoking while pregnant can have negative consequences, but could smoking also negatively affect one€™s ability to become pregnant? A study collected data on 678 women who had gone off birth control with the intention of becoming pregnant. Smokers were defined as those who smoked at least one cigarette a day prior to pregnancy. We are interested in the pregnancy rate during the first cycle off birth control. The results are summarized inTable 2.11.

(a) Is this an experiment or an observational study? Can we use these data to determine whether smoking influences one€™s ability to get pregnant? Why or why not?

(b) What is the population of interest?

(c) What is the proportion of women successfully pregnant after their first cycle (p̂)? Proportion of smokers successful (p̂_s)? Proportion of nonsmokers successful (p̂_ns)?

(d) Find and interpret (pÌ‚_ns €“ pÌ‚_s) the difference in proportion of success between non-smokers and smokers.

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Smoker Total 244 Non-smoker 206 337 Pregnant Not pregnant Total 38 434 97 135 543 678