From Seth Stephens-Davidowitz:
The Great Recession appears to have caused a significant increase in depression. In 2009 and 2010, there was a large increase in depression queries in states with large increases in unemployment, like Nevada, Florida and Alabama, compared with states that were little affected, like North Dakota and Arkansas. A 1 percentage point increase in the unemployment rate was associated with a 2 percent increase in depression queries.
What factors, besides unemployment, explain an area’s search rate for “depression”? I tested dozens of variables in many different categories. The strongest predictor by far: an area’s average temperature in January. Colder places have higher rates of depression, with the correlation concentrated in the colder months. The relationship between weather and mental health has been debated, but those debates have generally relied on “small” data. Google searches, the biggest data source we currently have, are unambiguous: when it comes to our happiness, climate matters a great deal.