Generalized linear model for total MADRS-S score and salivary melatonin levels at bedtime in patients (Model 1).

The relationship between low melatonin and high MADRS-S scores remains after including variables known as possible confounders (Model 2). First quartile denotes the quartile with lowest melatonin levels. Fourth quartile, with highest melatonin levels, is set as the reference. Season means summer vs. winter season.