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An important variant of the external validity problem deals with selection bias, also known as sampling bias—that is, bias created when studies are conducted on non-representative samples of the intended population. For example, if a clinical trial is conducted on college students, an investigator may wish to know whether the results ...
A distinction of sampling bias (albeit not a universally accepted one) is that it undermines the external validity of a test (the ability of its results to be generalized to the rest of the population), while selection bias mainly addresses internal validity for differences or similarities found in the sample at hand. In this sense, errors ...
Overmatching thus causes statistical bias. [13] For example, ... It may be regarded as a sampling bias in decreasing the external validity of a study, ...
Detection bias occurs when a phenomenon is more likely to be observed for a particular set of study subjects. For instance, the syndemic involving obesity and diabetes may mean doctors are more likely to look for diabetes in obese patients than in thinner patients, leading to an inflation in diabetes among obese patients because of skewed detection efforts.
There are five key principles relating to internal validity (study design) and external validity (generalizability) which rigorous impact evaluations should address: confounding factors, selection bias, spillover effects, contamination, and impact heterogeneity. [5]
Field experiments offer researchers a way to test theories and answer questions with higher external validity because they simulate real-world occurrences. [6] Some researchers argue that field experiments are a better guard against potential bias and biased estimators. As well, field experiments can act as benchmarks for comparing ...
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 ...
The experimenter may introduce cognitive bias into a study in several ways — in the observer-expectancy effect, the experimenter may subtly communicate their expectations for the outcome of the study to the participants, causing them to alter their behavior to conform to those expectations. Such observer bias effects are near ...