Hemorrhagic stroke in young women. Exercise 18.21 addressed data from a matched-pair case–control study on oral contraceptive use and thrombotic stroke in young women. The investigators also collected information on hemorrhagic stroke. Table 18.34 lists data for this outcome.

(a) Calculate the odds ratio for these data. Interpret the results.

(b) Break the match and rearrange the data to form a 2-by-2 cross tabulation for unmatched data. Calculate the odds ratio ignoring the match. How does this odds ratio compare to that of the (proper) matched-pair analysis?
TABLE 18.34 Data for Exercise 18.32. Thrombotic stroke and oral contraceptive case-control study. Data are matched pairs.