Because pain is a subjective sensation
, it is difficult to evaluate objectively in clinical trials.
Decreased salivary flow has been correlated with a subjective sensation
of dysphagia, and some studies have shown prolonged pharyngeal transit times.
Glare caused by natural lighting is usually studied in dark chambers lit with devices emulating a window: the photometric independent variables measured are correlated with the subjective sensation
of glare from the observers and turned into equations [Hopkinson 1972, Chauvel and others 1980, Iwata and others 1991].
When evaluating if sleep disorders are existent or not, experts try to draw on the subjective sensation
of the participants.