Smoking and survival
In the proportional Venn diagram,
The area of the rectangle for any combination of smoking, age and survival is proportional to the number of women in that combination.
Click any blue rectangle to read off the proportions of smokers and non-smokers dying in specific age groups. P(dead) is higher for smokers than non-smokers in each age group.
Select Group by smoker? from the pop-up menu to rearrange the shapes of the rectangles. The overall proportion of smokers dying is less than the overall proportion of non-smokers dying.
The relationship reverses because most older women were non-smokers, and older women also had a higher proportion of deaths.