Can someone with a stats background explain why the article claims there's a correlation? Those charts had R^2 values of .428, .344, and .403. I thought low R^2 values indicated no correlation.
Disclaimer: my statistics background consists entirely of one class (AP Statistics).
I think this is part of the answer to your question, nhebb, but also I think we might have some confusion about r. In my understanding, (which is also limited to only AP Statistics) r is the value representing how well correlated the two categories are, and r squared represents how much of the correlation the categories you're using at that time accounts for. Does that sound right?
In my experience, people with advanced education work more hours. Doctors, lawyers, engineers, programmers, accountants,... the list of professions that require a lot of 40+ hour work week goes on. Most lower wage jobs, by contrast, work straight 40 hour work weeks
Also, is the data adjusted for cost of living? Why are they using average wages instead of median wages?
Overall, it just looks like a crappy study that doesn't lead to tangible insights.