What is the difference between internal and external validity?
http://www.une.edu.au/WebStat/unit_materials/c2_research_design/validity_internal_external.htm
http://www.edpsycinteractive.org/topics/intro/valdgn.html
Internal validity and external validity are two concepts related to research design and the extent to which study results can be generalized to different populations or situations.
Internal validity refers to the degree to which a study accurately demonstrates a cause-and-effect relationship between variables. It assesses whether the observed changes in the dependent variable are actually due to the manipulation of the independent variable and not caused by other factors.
To establish internal validity, researchers must carefully control for potential confounding variables, use random assignment of participants to different conditions, and ensure a strong experimental design. This can be achieved by using control groups, blinding procedures, randomization, and proper measurement techniques.
External validity, on the other hand, refers to the extent to which the findings of a study can be generalized to real-world settings or populations beyond the specific sample used in the study. It assesses whether the results from a study can be applied to other people, places, or times.
To enhance external validity, researchers must ensure that the sample used in the study is representative of the target population, provide a detailed description of the study procedures, and use diverse samples to capture the variability of the population of interest.
In summary, internal validity is concerned with the accuracy of the study's results within the study itself, while external validity focuses on the generalizability of those results to other populations or situations.