In the article "coffee, caffeine, and risk of depression among women" in the september 2011 edition of the archives of internal medicine, researchers investigated the relationship between caffeine consumption and depression among women.

the participants in this study were older, with substantially lower rates of depression when compared to female teens. researchers compared two groups of women (among others) in this study: those who do not drink coffee and those who routinely drink 4 or more cups of coffee each day.

for the following question, a coffee drinker is a woman who drinks four or more cups each day.

in the sample of 920 coffee drinkers, researchers identify 40 as depressed. among the sample of 1100 non-coffee drinkers, 69 are depressed. let coffee drinkers be sample 1 and non-coffee drinkers be sample 2.

what is the difference between the corresponding sample proportions, p1-p2 ?

a) 0.019
b) 0.19
c) 0.019
d) 0.19