Do sunny places have less depression?

Grey winters are often blamed for low mood, and across US counties the numbers seem to agree: where winters are sunnier, fewer adults have been told they have depression. But sunny counties differ from grey ones in more than the weather. Once you compare counties with the same mix of people, almost nothing is left.

The two measures

Winter sunlight is how much sunlight reaches the ground on an average day from December to February, estimated from satellites by NASA. Each county takes the value for the square of land about 100 km across around where most of its people live, so nearby counties often share a value. Depressionis the share of adults who have ever been told by a doctor or nurse that they have it, from CDC’s county estimates.

Sunnier winters, less depression

Each dot is a county. Across 2,934 counties, the sunnier the winter, the less depression: −0.29. Comparing counties alike in how crowded, rich and educated they are makes the link a little stronger, at −0.37. So far it looks like a real pattern.

The chart leaves off the 105 most extreme counties so the rest can be seen. Every figure on this page uses all of them.

Every figure here is r: how closely two measures rise and fall together, from −1 (one goes up as the other goes down) to +1 (they rise together). 0 means no link.

Then it fades, one check at a time

Comparing counties only with others in their own state leaves −0.29. Sunny places are also warm places, so the next step holds temperature equal as well: −0.24. Sunny places are often older, and older adults report depression less often. Allowing for age leaves −0.22.

The last step allows for the share of residents who are Hispanic. The sunniest counties, in the Southwest, have the most Hispanic residents, and Hispanic adults are told they have depression less often than others. With that held equal, the link is −0.04: almost nothing, across the 2,702 counties with all of these figures.

The same with bad mental health days

A diagnosis needs a visit to a doctor, so the check is repeated with a measure that does not: frequent mental distress, the share of adults who say their mental health was not good on 14 or more of the last 30 days. Within states and with temperature held equal, sunnier counties have a little less of it, at −0.26 after allowing for age. Allowing for the Hispanic share leaves −0.06.

A check that does not rely on a model

CDC’s county figures are estimates from a statistical model. It starts from a phone survey and uses each county’s age, sex and racial mix as inputs. So a county with more Hispanic residents is given a lower estimate partly for that reason alone. The survey itself is asked directly in every state, so the steps are repeated across the 49 states with the survey’s own depression figure. The same story comes out: −0.46 after the usual adjustment, −0.14 with temperature held equal, and −0.07 after age and the Hispanic share.

What it might mean

The data does not show that winter sunshine has no link to mood. Some people’s mood dips in the dark months, and that is well studied in people themselves. What it shows is that the gap between sunny and grey counties in these figures is mostly a gap in who lives there. Any part left for sunshine is too small to see at the scale of whole counties. Being told you have depression also depends on seeing a doctor, and that is less common in some groups than others.

What this cannot tell you

• It describes counties and states, not people. It cannot say how sunshine affects any one person.
• Sunlight comes from a coarse grid, so it shows broad regions better than single counties.
• The county depression figures are model estimates, not counts of people.
• A link is not proof that one thing changes the other, and neither is the lack of one.

See the full figures for winter sunlight vs depression, and how holding sunshine equal changes other links.

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• Where more women work, people drink more
• In tight-knit counties, fewer people move in or out
• Friendships across income lines, and how far poor children climb

These articles describe places, not people, and show links, not causes. Every article on PlaceStats.