As the quote from Gene Glass suggests, research synthesis used to be a subjective
process with little protection against bias favoring the perspective of the preparer.
However, since Glass’s characterization, methods for the retrieval, integration, and
interpretation of research literatures have undergone enormous change. Today, the
approach suggested by Glass is widely viewed as unacceptable and certainly
inappropriate for informing decisions regarding the adoption of social programs and
policies. Instead, research synthesis now has its own methodological techniques and
decision rules, all meant to help synthesists produce an unbiased estimate of what the
cumulative evidence says.