One of the threats to internal validity presented in the experiment is history. It is critical to appreciate the fact that events found outside the study can to a greater extent affect the responses of various participants in the course of the study. The difference observed in the pre, and post-test scores could be attributable to time and not necessarily due to the participation in the therapy discussed. Another threat to internal validity that becomes apparent as the study continues is due to maturation. Participants tend to change or evolve as the measurement or the experiments proceed. Since the study is about Post-traumatic stress disorder (PTSD) among the military, it is worthy to note that the respondents might mature as a result of various forces in the society or also as a result of the normal development process. Also, another essential threat to internal validity that must be taken into consideration is mortality in the experiment. The participants engaging in this type of sensitive research have a higher likelihood of dropping out.
Confounding factors could also be a basis of a threat to the internal validity. It is critical to note that PTSD being a mental disorder, it could also manifest in an individual as a result of other factors unrelated to the fact that the person was military personnel. Selection bias could also jeopardize the internal validity given that only those with consent would be selected for the study. Furthermore, it is also vital to note the effects of repeated testing that would put the respondents in a conditioned state of knowing that they are under test. Finally, the last test for internal validity is the instrument change. The constant alteration of the changing procedures could heavily impact the outcomes of the tests.
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External Validity
One of the most notable threats to external validity is the effect of pretesting. Conducting the pretest to determine the efficacy of the experiment could impact the responsiveness of the military respondents used in the study. Secondly, because the study does not employ a random sampling, there is a threat to external validity with regards to the effect the criteria of inclusion and exclusion. The selection of the respondents used in the study follows certain criteria with a majority being discharged veterans documented by the Veteran Affairs (VA). Also, only consented participants are required in the study. As such, the threat of inclusion and exclusion becomes a reality. Because the respondents are exposed to various experiments at given times, there is a prospect of multiple experiment interference which is a major threat to the external validity. The results found in the previous become a major threat to the result under investigation.
It is also natural that during this experiment, most veterans or military respondents are aware of their engagement in a research experiment. The respondents in the study are mostly those discharged from a mental institution with many aware that veterans are always associated with PTSD. As such, the type of threat to external bias that could depict itself here is the reactions to an experimental arrangement where the participants are aware of the experiment. The situation of the respondents such as treatment conditions as seen with the choice of discharged patients is likely to affect the experiment. Other conditions that could also impact the study include environmental factors such as noise and lighting among others. The cause-effect relationship could also be watered through the pretest and posttest effects conducted on the respondent. Finally, the nature of the interviewer with regards to the nature of the question could also be a source of the external threat.
