SYNTHESIZING RESEARCH RESULTS:
All sciences progress by the gradual accretion of knowledge. Although surely inspired, Einstein's classic formula relating energy, mass, and velocity was not drawn out of thin air. His was an enormously creative insight based on a synthesis and extension of the available knowledge of the time (Clark, 1971; Kuhn, 1970). Over the years, social scientists have relied on a similar process of intuition and integration of prior findings to develop new insights, which sometimes lead to the accumulation of yet more knowledge. To the extent that the existing literature on a phenomenon is accurate and that we have surveyed it comprehensively and fairly, we can develop an understanding of the structure of interrelationships that underlie it. Current knowledge is the foundation of future discoveries. In the past, this integrative, constructive process was based on a careful reading and interpretation of research results (a narrative review, as Johnson and Eagly, 2000, termed it) combined with creative theory-based insights.
This time-honored integrative process has been supplemented in recent years by the development of methods of quantitative synthesis, sometimes termed meta-analysis (i.e., a summary analysis of cumulated, earlier analyses). These methods allow for the quantitative assessment of factors that affect, or help define, a given phenomenon or construct. The earlier, narrative approach has served us well, but its critics suggest that it is prone to important shortcomings, including (a) narrative analysts' occasional tendency to fail to survey the existing knowledge base completely1, (b) the lack of clearly stated rules for inclusion or noninclusion of studies in their analyses, and (c) the failure to use a common statistical metric to combine findings across different studies. A competent, systematic meta-analysis is intended to avoid all of these problems and thereby develop a more comprehensive understanding of a construct, or of a relationship between variables. The ultimate goal of such analyses is to construct a secure foundation on which to build a____________________