This study examines what sources of evidence are used in intervention selection and what changes in belief occur when performance improvement professionals make these decisions. Sixty‐one certified performance technologists completed a dynamic, web‐delivered questionnaire in which they provided a general assessment of intervention success (Pr1), then responded to 12 performance improvement scenarios by selecting an intervention, providing a prior probability, receiving additional evidence, giving a posterior probability (Pr3), indicating whether the initial intervention was still preferred, and making a subsequent choice if not. Findings bolster the long‐standing concern about the technical nature of performance improvement, and practitioners are strongly encouraged to approach intervention selection as a decision, where their intervention preferences and beliefs of likely success are carefully adjudicated on the basis of the evidence they obtain. Future research with other types of performance improvement practitioners, replication studies, longitudinal, structural equation modeling, externally verifiable probabilities, and natural environments are recommended.