External Validity - External, Internal, and Ecological Validity

External, Internal, and Ecological Validity

In many studies and research designs, there may be a "trade-off" between internal validity and external validity: When measures are taken or procedures implemented aiming at increasing the chance for higher degrees of internal validity, these measures may also limit the generalizability of the findings. This situation has led many researchers call for "ecologically valid" experiments. By that they mean that experimental procedures should resemble "real-world" conditions. They criticize the lack of ecological validity in many laboratory-based studies with a focus on artificially controlled and constricted environments. External validity and ecological validity are closely related in the sense that causal inferences based on ecologically valid research designs often allow for higher degrees of generalizability than those obtained in an artificially produced lab environment. However, this is not always the case: Some findings produced in ecologically valid research settings may hardly be generalizable, and some findings produced in highly controlled settings may claim near-universal external validity. Thus, External and Ecological Validity are independent – a study may possess external validity but not ecological validity, and vice-versa.