But how they relate over time is less crystal clear.

‘Some discovered that depression and obesity go hand-in-hand, while some didn’t observe that connection. We tried to take the next step in clarifying this link by looking at an example of youth that people followed from ages 11 to 24.’ This method improves on past research that included recurrence or persistence of depression and obesity instead of focusing on the onset of every disorder. Participants in Marmorstein's study were assessed at ages 11, 14, 17, 20, and 24 by using height and weight measurements and clinical, interview-based diagnosis of major depressive disorder. The researchers looked specifically for onsets of either disorder by age 14, between the age groups of 14 and 20, and between age groups 20 and 24.The finding of the superiority of saline to soap was not robust to a sensitivity analysis that assumed that individuals in the saline group who had been lost to follow-up acquired a risk of event that was doubly high as the chance among those with complete follow-up. This analysis reduces our power of inference that soap is normally inferior, nonetheless it does not really undermine the conclusion that soap is normally no better than saline.