The sources below will help you answer the questions: What helps? What harms? Under what conditions? At what costs?
Anyone considering the implementation of a program designed to create a desired change (increasing reading skills, reducing recidivism among juvenile offenders, a mindfulness based stress reduction program for the elderly, policy intervention) needs evidence to justify a proposal for doing so. This means becoming familiar with the terms randomized controlled trials (the gold standard for determining cause and effect), systematic reviews, and meta-analyses, which provide the highest levels of evidence about specific interventions.
Systematic review: This is a methodical and thorough literature review focused on a particular research question. It's aim is to identify and synthesize all of the scholarly research on a particular topic in an unbiased, reproducible way. It may involve a meta-analysis (see below).
Meta-analysis: This is a type of research study that combines or contrasts data from different independent studies in a new analysis in order to strengthen the understanding of a particular topic. There are many methods, some complex, applied to performing this type of analysis.
“The goal of qualitative research is the development of concepts which help us to understand social phenomena in natural settings, giving due emphasis to the meanings, experiences and views of all the participants” Pope and Mays, BMJ 1995; 311; 42-45