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Ex post facto recruitment methods are not considered true experiments, due to the limits of experimental control or randomized control that the experimenter has over the trait. This is because a control group may necessarily be selected from a discrete separate population. This research design is thus considered a quasi-experimental design.
External validity is the validity of applying the conclusions of a scientific study outside the context of that study. [1] In other words, it is the extent to which the results of a study can generalize or transport to other situations, people, stimuli, and times.
Internal validity, therefore, is more a matter of degree than of either-or, and that is exactly why research designs other than true experiments may also yield results with a high degree of internal validity. In order to allow for inferences with a high degree of internal validity, precautions may be taken during the design of the study.
In other words, the relevance of external and internal validity to a research study depends on the goals of the study. Furthermore, conflating research goals with validity concerns can lead to the mutual-internal-validity problem, where theories are able to explain only phenomena in artificial laboratory settings but not the real world. [13] [14]
Ecological validity, the ability to generalize study findings to the real world, is a subcategory of external validity. [6] Another example highlighting the differences between these terms is from an experiment that studied pointing [7] —a trait originally attributed uniquely to humans—in captive chimpanzees. This study certainly had ...
It is a significant threat to a study's internal validity, and is therefore typically controlled using a double-blind experimental design. It may include conscious or unconscious influences on subject behavior including creation of demand characteristics that influence subjects, and altered or selective recording of experimental results themselves.
Simply put, pragmatic validity looks at research from a prescriptive-driven perspective. Solutions to problems that actually occur in the complex and highly multivariate field of practice are developed in a way that, while valid for a specific situation, need to be adjusted according to the context in which they are to be applied.
Natural experiments leverage events outside the researchers' and subjects' control to address several threats to internal validity, minimising the chance of confounding elements, while sacrificing a few of the features of field data, such as more natural ranges of treatment effects and the presence of organically formed context. [16]