Meta-Analysis of Experimental Manipulations: Some Factors Affecting the Velten Mood Induction Procedure
Manipulation validity may be influenced by many factors, including specific aspects of experimental procedure. Meta-analysis is an ideal tool for assessing factors that influence manipulations because it is capable of equating, combining, and gauging the impact of different experimental procedures on a given manipulation. This use of meta-analysis is demonstrated by meta-analyzing experiments employing the Velten mood manipulation. This manipulation has been criticized for creating experimental demand. Procedures relevant to experimental demand include whether an honest or deceptive cover story is used and whether a self-report or non-self-report manipulation check measure is used. Effect sizes are smaller when a deceptive (vs. honest) cover story is used and when a non-self-report (vs. self-report) manipulation check measure is used. Discussion concerns how the Velten manipulation may be compromised and how meta-analysis may be employed to evaluate factors influencing manipulation validity.