One of the first experimental studies to demonstrate that happiness increases charitable behavior was conducted by Isen and Levin (1972), who showed that after experiencing positive events (such as receiving cookies, or finding a dime left in a payphone), participants were more likely to help others: Thus, people who felt good were more likely to provide help. Replicating this effect in a different context, Aderman (1972) induced either an elated or depressed state by having participants read statements designed to induce these moods. Participants in a positive mood were more likely to help with a favor to the researcher during the experiment, and even promised to help by participating in a second experiment. Other positive mood states have also been shown to increase altruism; feelings of competence, for example, have been shown to increase helping and volunteering behavior (Harris & Huang 1973; Kazdin & Bryan 1971), as has succeeding on tasks (Isen, 1970).