Different research designs contribute to evidence-based practice, and different research designs are better suited to different types of questions.
Clinical observation (including individual case studies) and basic psychological science are valuable sources of innovations and hypotheses (the context of scientific discovery).
Meta-analysis is a systematic means to synthesize results from multiple studies, test hypotheses, and quantitatively estimate the size of effects.
Qualitative research can be used to describe the subjective, lived experiences of people, including participants in psychotherapy.
Randomised Controlled Trials (RCTs) are the standard for drawing causal inferences about the effects of interventions (context of scientific verification).