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External validity is the validity of generalized (causal) inferences in scientific research, usually based on experiments as experimental validity.〔Mitchell, M. & Jolley, J. (2001). ''Research Design Explained (4th Ed)'' New York:Harcourt.〕 In other words, it is the extent to which the results of a study can be generalized to other situations and to other people.〔Aronson, E., Wilson, T. D., Akert, R. M., & Fehr, B. (2007). Social psychology. (4 ed.). Toronto, ON: Pearson Education.〕 ==Threats to external validity== "A threat to external validity is an explanation of how you might be wrong in making a generalization."〔Trochim, William M. The Research Methods Knowledge Base, 2nd Edition.〕 Generally, generalizability is limited when the cause (i.e. the independent variable) depends on other factors; therefore, all threats to external validity interact with the independent variable - a so-called background factor x treatment interaction. * Aptitude–treatment Interaction: The sample may have certain features that may interact with the independent variable, limiting generalizability. For example, inferences based on comparative psychotherapy studies often employ specific samples (e.g. volunteers, highly depressed, no comorbidity). If psychotherapy is found effective for these sample patients, will it also be effective for non-volunteers or the mildly depressed or patients with concurrent other disorders? * Situation: All situational specifics (e.g. treatment conditions, time, location, lighting, noise, treatment administration, investigator, timing, scope and extent of measurement, etc. etc.) of a study potentially limit generalizability. * Pre-test effects: If cause-effect relationships can only be found when pre-tests are carried out, then this also limits the generality of the findings. * Post-test effects: If cause-effect relationships can only be found when post-tests are carried out, then this also limits the generality of the findings. * Reactivity (placebo, novelty, and Hawthorne effects): If cause-effect relationships are found they might not be generalizable to other settings or situations if the effects found only occurred as an effect of studying the situation. * Rosenthal effects: Inferences about cause-consequence relationships may not be generalizable to other investigators or researchers. Cook and Campbell made the crucial distinction between generalizing ''to'' some population and generalizing ''across'' subpopulations defined by different levels of some background factor. Lynch has argued that it is almost never possible to generalize ''to'' meaningful populations except as a snapshot of history, but it is possible to test the degree to which the effect of some cause on some dependent variable generalizes ''across'' subpopulations that vary in some background factor. That requires a test of whether the treatment effect being investigated is moderated by interactions with one or more background factors. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「External validity」の詳細全文を読む スポンサード リンク
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