Threats to external validity compromise the confidence in asserting that the results of the study can be generalized to and between individuals, settings, and under the temporal perspective.
External validity is compromised by low fidelity by not being able to draw conclusions about the generalisability of factors found to be responsible for any effects.
23 We agreed on some flexibility for inclusion in this feasibility study because the FINDRISC algorithm includes a heavily weighted family history question and validity is compromised where data on family history are unavailable.
One view is that fidelity should be strictly maintained with adherence to all aspects of the intervention protocol, whereas another view is that interventions should be flexible to change when implemented in different settings, but not so flexible that validity is compromised.
If not, the data-validity is compromised, as the data gathered will be influenced by the researcher's interaction.
It is generally accepted that the measures usually taken to increase internal validity may compromise external validity/generalizability [ 51, 69, 70], simply because they restrict the range of conditions under which the relationship between dependent and independent variables is being tested.
The correlation is however compatible with validity, and the argument for validity would be compromised if such a correlation not present.
A high external validity may therefore compromise internal validity, particularly in those cases where study designs reflect everyday conditions but fail to control other influences on the outcomes.
Prospective observational study designs may overcome some of these limitations, but attention is required to ensure that internal validity is not compromised.
Non-random sampling means external validity is also compromised.
However, missing values might have compromised validity of or findings.
