Here is a very precise explanation (by Professor Matt Might) in a graphic way.![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh2JKR8yn1fkSeStVhf8I3Jf9Exf1Ws8Y12F7vsoYXxx-xvirMHp1RQ1o8upfXXKTzVQkqkEIfYjwMZqP6fAd1Q-srHnmG_ngDV_ztv_GH-0WR3tJhZmBcXAAREVJfLrMczFa2hn4GYhQ0/s320/PhDKnowledge.011.jpg)
obs. This post is a replay from a 2010 post.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh2JKR8yn1fkSeStVhf8I3Jf9Exf1Ws8Y12F7vsoYXxx-xvirMHp1RQ1o8upfXXKTzVQkqkEIfYjwMZqP6fAd1Q-srHnmG_ngDV_ztv_GH-0WR3tJhZmBcXAAREVJfLrMczFa2hn4GYhQ0/s320/PhDKnowledge.011.jpg)
obs. This post is a replay from a 2010 post.
Structured Procrastination on Cities, Transport Policy, Spatial Analysis, Demography, R
"The reasons for the decline remain unclear, but researchers offered possible explanations, including a spike in prescription drug overdoses among young whites, higher rates of smoking among less educated white women, rising obesity, and a steady increase in the number of the least educated Americans who lack health insurance."In case you want to read the published paper.