Expectancy influences the operation of personality on behavior.

The authors investigated the moderating effect of expectancies on personality for 2 different addictive behavior processes: (a) drinking and (b) binge eating and purging characteristic of bulimia nervosa. Study 1 found that positive expectancies for social facilitation from drinking moderated the effect of extraversion on drinking behavior among undergraduate men and women. Study 2 found that the expectancy that eating will help manage negative affect moderated the effect of trait urgency on bulimic symptoms among undergraduate women. Thus, the relationships of the trait risk factors to these 2 addictive behaviors are stronger if one also holds certain expectancies for reinforcement from those behaviors.