The inability to manipuate variables of interest has led to a preponderance of ex post facto and correlational studies in the discipline. In an ex post facto study, two or more groups are compared after an event of interest has occurred. The researcher has no control over assignment to groups or the nature of the treatment. While the researcher may go to some effort to match firm in the two groups, the lack of random assignment and control threatens the internal validity of the study. Interestingly, the statistical tests do not vary between experimental and pseudo- experimental designs, leading to a tendency to attribute a scientific status to the results.
Correlational studies are much more common in the field.
In this approach a dependent variable is regressed on one or more independent variables. The central issue lies in the fact that causation implies correlation but correlation does not imply causation. The upshot is that even in the highly unlikely event that a researcher could convince firms to re-enact their strategic actions, small differences between the two studies that are beyond the researcher's control could destroy the validity of the study. The inability to directly observe and manipulate key variables, particularly a company's strategy, has hindered strategy researchers from developing better explanations and predictions. The dynamic nature of strategy suggested by complex systems theory also represents a problem for scholars trained in static analysis and comparative static analysis.