Megan Traffanstedt and Dr. LoBello, in collaboration with Dr. Sheila Mehta, searched the CDC’s survey results for links between high scores on the depression screen and particular seasons or latitudes. The researchers also looked to see if high latitudes combined with the winter season to raise the frequency of depressed answers more than high latitude or winter alone. Hours of sunlight at a given location and date are available from the U.S. Naval Observatory, so the researchers even tested for links between depression scores and hours of sunlight on the day a score was collected. If light is responsible for SAD, then looking at hours of sunlight should be a sensitive way to detect people with SAD among the general population, they thought.So why has the scientific community settled on the existence of SAD?
Instead, the CDC survey revealed no evidence for seasonal affective disorder. The researchers were wary of overlooking SAD trends among the huge non-SAD population, so they reanalyzed answers from a subset of people who classified as depressed at the time of the survey. Still no sign of SAD. No seasonal or light-dependent increases appeared in the depression measures. We might wonder if something was wrong with the phone study, but other well-established trends appeared in the survey data, such as higher rates of depression for women and the unemployed. The fluctuation in depression from SAD was either nonexistent or undetectable.
One problem lies with the questions being asked. Those questions typically used to screen for SAD, while very specific, are also incredibly leading. Imagine you are answering a battery of questions about how your mood, weight, appetite vary over the year, then filling out charts to compare your habits over the the seasons. You are asked to consider at which time of the year you gain or lose weight, sleep or eat less. Using this standard assessment for SAD, you might reconsider whether you have a yearly mood cycle after all. The CDC telephone survey did not ask the usual SAD questions but relied on eight questions commonly used to screen for major depression. These questions ask about topics not covered in standard SAD assessments — hopelessness, lack of pleasure in activities, trouble concentrating — and concern the past two weeks rather than the past fifty-two. It is much easier to recall how you felt in the recent past than to remember how you felt last October. Our memories can smudge and blot over time, especially if we expect a certain pattern.Confirmation bias. We think winter, and darkness are a reason for depression, so we answer questions that way.
This introduces another problem with SAD studies: expectations. Even hearing about the “winter blues” in popular culture could plant confirmation biases, encouraging potential patients (or researchers) to find evidence of SAD whether it exists or not. Our preconceptions are always hard at work, so survey data collected without any mention of seasonal mood disorders is a safer bet for avoiding biases. A person experiencing major depression episodes in the winter might need therapy for SAD or they might need therapy to cope with holiday-time stresses.So, if you're depressed in winter, before daylight savings time, you need to find something else to blame. I blame lack of fishing.