This meta-analysis demonstrated that film clips can be used reliably to induce negative and positive mood states. For both states, the effect size levels were quite high. The use of film clips provides interesting physiological results, as indicated by significant increases in heart rate, blood pressure, frontal EEG electrodes, and photoresponses, cortisol, and testosterone. Last, the fact that a large number of film clips were required to elicit positive mood states is an important finding. Considering that film clips induce emotions, especially negative states, and that they act fast and effectively, this finding is not surprising.
Naturally, the data indicate limitations of the present meta-analysis. First, there are only ten categories of film clips currently used for mood induction research. We encourage researchers in the field to continue validating and expanding film clip databases to provide more 'out-of-the-box' solutions. Second, the analysis lacked consideration of the quality of the studies. Larger samples and more researchers using randomized and double-blind randomized studies are needed to increase the robustness of the work. Third, the data on affect avoidability may be influenced by improvements in the ability to measure affect. Finally, the present meta-analysis is based on the assumption that film clips are the most effective stimuli for inducing positive and negative mood states. Nevertheless, we believe that the present meta-analysis points to a new and interesting direction for mood induction research. In the field of affective information processing, is it possible that the most effective stimulus is not the most threatening, but the most valuable information? Based on the results of this meta-analysis, we might consider the case of brief exposure to an emotion-eliciting film clip. Such an exposure would not have the effects of exhausting a person's emotional resources, creating more difficult for the subject to subsequently adapt to a new emotional state, or risking long-term negative health consequences, as might be the case with prolonged exposure to the same stimulus or to many stimuli. Indeed, the most effective stimuli for inducing a mood state may not be the most stressful ones, but those that are more valuable (useful information for the emotional processing), and that facilitate communication with others. d2c66b5586