The equation factors in cold and cloudy weather. Add this to credit card bills arriving with Christmas debt and multiply by the time passed since the holidays. This is also the time when most people have given up on New Year's resolutions. Divide all this by low motivation and the need to take action.
Dr. Jonathan Henry of the Clinton, Eaton, and Ingham County Mental Health Department says he's not sure the equation is proven, but all the elements do lead to the winter blues.
The formula was made to help travel companies. It shows when people are most likely to book vacation getaways.