Psychology is a core aspect that influences all design.
In this article from Medgadget, Matt Loper tells how a particular human psychological trait is the key to an app that encourages compliance with medical treatment regimens.
Wellth is the app that Loper’s company has created. It encourages adherence not by giving something as a reward for correct behavior, but rather by taking something away as a consequence of bad behavior.
Given a choice between losing a benefit we have and gaining a benefit we don’t yet have, we much prefer keeping our current benefit. Wellth harnesses this loss-aversion trait by crediting the app user $150 at the start of a 90-day tracking period (with the goal of establishing a habit of adherence). For each instance of non-compliance (not taking your med), the patient loses $2. After the 90-day period, they keep whatever is left of the $150.
Using this technique, Wellth has seen a remarkable increase in adherence rates among the patients that sign-up to participate. A great example of how applying psychology can influence outcomes.