A well known Walmart retail case study - the story of beer and diaper. 55% of people who buy diapers also buy beer; dig a little deeper - the buyers are mostly working males in the age group of 30 to 45, and they mostly buy the two items together on Fridays and Saturdays. Clean story - as working fathers babysit (read made to) during the weekends, they need some fuel. What do we do with it? To start off, we keep them together; those fathers who are not so much into spiritual upliftment, would pick up the beer if they don't have to look for it. Bingo: Beer sale goes up by 60%.
This was 2004. Six years later when a certain someone moved out of town for a couple of months, I hit upon a more interesting correlation between these two items. When I return home after work, a unused diaper on the side table in my bedroom catches attention without fail.... and? Same story: beer consumption significantly goes up.