In this regard, Kahle and Riley note that, "Traditionally, causality is established through strict control and randomization over all other factors while experimentally manipulating the variable or variables in question" (2004, p. 165). Finally, Gliner and Morgan (2000) report that the internal validity (discussed further below) and the ability to infer causality based on the results of a study can be enhanced through the random assignment of the participants to intervention vs. control groups.
b.
What is meant by internal validity and external validity in leadership research and discuss three factors within each (internal and external) validity factor?
Internal validity. According to Chandler and Lyon, generally speaking, "Validity refers to the establishment of evidence that the measurement is actually measuring the intended construct. Measures can be reliable without being valid, but cannot be valid without being reliable" (2001, p. 102). With respect to internal validity, this term refers to the degree of validity of the assertions being made by a researcher concerning the effects of the independent variable(s) on the dependent variable(s) (Pedhazur & Schmelkin, 1991). According to Pedhazur and Schmelkin, "In the broadest sense, this can be stated in the form of the question: Is what has taken place (i.e., the phenomenon observed) due to the variables the researcher claims to be operating (e.g., manipulated variables), or can it be attributed to other variables?" (1991, p. 224). By taking steps to ensure the internal validity of a study's design, researchers can rule out alternative explanations for the results they obtain. In this regard, Pedhazur and Schmelkin add that, "In essence, the validity of the answer to this question depends on the plausibility of alternative answers, that is, alternative explanations. It follows that internal validity is the sine qua non-of meaningful research" (1991, p. 224).
Internal validity can be enhanced by ensuring there are relevant controls in place, but researcher bias remains a confounding factor in the interpretation of the results that emerge from any study (Berg, 2007). For example, according to Pedhazur and Schmelkin, "Other things equal, the more powerful the controls one exercises, the more internally valid the study. The tendency to overlook evidence that goes counter to one's expectations and hypotheses, or to misinterpret, even rationalize, such evidence, is quite common" (1991, p. 225). A number of threats to internal validity exist, including those described in Table 1 below.
Table 1
Threats to Internal Validity
Threat
Description
History
This threat includes events that took place in the course of a study that might have affected its outcome. Whether a given event poses a threat to the internal validity of a study depends on the specifics of the study.
Maturation
This type of threat refers to changes that people being studied undergo with the passage of time, including growing older, gaining experience, becoming tired, hungry, and the like. The concern is that responses (e.g., learning, motivation, aggression, concentration) attributed to treatments may be, in part or wholly, due to such maturational processes. It is also possible for maturation to interact with treatments.
Testing
When people are measured several times on the same variable, their performance may be affected by, among other things, practice, memory of earlier responses, sensitization and/or conjectures regarding the purpose of the research and the expectations of the researcher. For example, given a pretest, followed by some treatments, and then a posttest, observed changes in, say, learning, attitudes, empathy, and altruism, may be a consequence of the pretest and/or the interaction between the pretest and the treatments
Instrumentation
Internal validity is compromised when differences in outcomes of different treatments may be attributed, to a greater or lesser extent, to aspects of the instruments used. This may occur when, for example, measures believed to be equivalent are not equivalent (e.g., they tap somewhat different competencies, orientations, or they differ in difficulty, in appeal). Another example would be cosmetic changes in instruments, which in actuality constitute changes in what they are measuring. A related example is one in which no changes are made in the instruments, but the researchers become more proficient in using them in the course of the study
Source: Pedhazur & Schmelkin, 1991, p. 225
External validity. According to Neuman, external validity refers to "the ability to generalize from experimental research to settings or people that differ from the specific conditions of the study" (2003, p. 535). Likewise, Gliner and Morgan (2000) report that, "External validity is an aspect of research validity that depends in part on the quality of the sample. External validity asks the question...
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