1. An apparatus comprising: a target data acquiring section operable to acquire target data serving as an examination target, the target data output by a plurality of sensors; a calculating section operable to calculate, for each of a plurality of sensor groups that each include at least two sensors among the plurality of sensors, a degree of outlierness of the target data relative to a reference data distribution of output from the sensor group; and an estimating section operable to estimate at least one sensor among the plurality of sensors to be a source of outlierness, based on a comparison of the degrees of outlierness of the sensor groups that include the at least one sensor to the degrees of outlierness of the sensor groups that lack the at least one sensor.