Postnatal depression affects approximately 8–15% of new mothers. One theory about the onset of postnatal depression predicts that it may result from the stress of a complicated delivery. If so, then the rates of postnatal depression could be affected by the type of delivery. A study (Patel et al. 2005) of 10,934 women compared the rates of postnatal depression in mothers who delivered vaginally to those who had voluntary cesarean sections (C-sections). Of the 10,545 women who delivered vaginally, 1025 suffered significant postnatal depression. Of the 389 who delivered by voluntary Csection, 48 developed postnatal depression.

a. Draw a graph of the association between postnatal depression and type of delivery. What is the pattern in these data?

b. How different are the odds of depression under the two procedures? Calculate the odds ratio of developing depression, comparing vaginal birth to C-section.

c. Calculate a 95% confidence interval for the odds ratio.

d. Based on your result in part (c), would the null hypothesis that postpartum depression is independent of the type of delivery likely be rejected if tested?

e. What is the relative risk of postpartum depression under the two procedures? Compare your estimate to the odds ratio calculated in part (b).