In a 2002 empirical study, researchers Tara MacDonald and Alanna Martineau investigated the effect of female university students' moods on their intentions to have unprotected sexual intercourse. They discovered that experiencing a negative mood increased intentions to engage in unprotected sex, but this effect was exclusively observed among students with low self-esteem. Conducting this research required the practical application of psychological measurement to quantify several intangible variables, specifically requiring the researchers to accurately measure each participant's self-esteem, successfully assess their mood after an experimental manipulation (thinking negative thoughts), and gauge their behavioral intentions regarding unprotected sex.