While the study approximates the form of a quasi-experimental study, the use of secondary data
weakened our ability to achieve a true quasi-experimental research design. We draw upon Cook
and Campbell’s (1979) criteria for assessing quasi-experimental research by highlighting the following
limitations of the current study.
Some of the samples employed in the pre- and post-NEA eras were not random and could
therefore be subject to distortion arising from different characteristics of the samples.
During the 10-year duration of policy implementation following the passage of the NEA,
other factors such as change in the composition of the population of principals could have
impacted the results.
Lack of teacher data in the 2008 study limits the construction of the instructional leadership
profiles to a single source (that is, the principals) and reduced the power of our comparisons
across the two time periods.
Use of secondary data meant that the researchers had to rely on the use of those statistics
reported in the dissertation studies.
These limitations in the research design imply the need for caution in making attributions of
causality concerning changes in principal role behaviour. We will discuss the limitations again
when we interpret the results of the study.