In psychiatric research, machine learning algorithms are being used to better define depression and to make predictions about which patients might respond to a given treatment. By “mining” data from larger datasets, researchers have been trying to find biomarkers — measurable biological indications — of depression. The thought is that researchers could teach a computer how to identify patterns in data from patient-reported surveys, demographic data, cognitive assessments, and even neuroimaging studies correlating blood oxygenation levels to brain activity in specific regions.To do this, scientists first input a subset of patient data and adjust their algorithm to reliably distinguish healthy versus control subjects or, in the case of treatment outcomes, responders from non-responders. They can then figure out which features in the data best help the computer “learn,” make sure that their algorithm only incorporates those data features, and validate their method by testing how accurately it can make predictions about the rest of the patients, whose data it has not yet taken into account.