Briefly define internal and external validity

What will be an ideal response?

Internal validity refers to whether the manipulation of the independent variables or treatments actually caused the observed effects on the dependent variables. Thus, internal validity examines whether the observed effects on the test units could have been caused by variables other than the treatment. If the observed effects are influenced or confounded by extraneous variables, it is difficult to draw valid inferences about the causal relationship between the independent and dependent variables. Internal validity is the basic minimum that must be present in an experiment before any conclusion about treatment effects can be made. Without internal validity, the experimental results are confounded. Control of extraneous variables is a necessary condition for establishing internal validity.

External validity refers to whether the cause-and-effect relationships found in the experiment can be generalized. In other words, can the results be generalized beyond the experimental situation and, if so, to what populations, settings, times, independent variables, and dependent variables can the results be projected? Threats to external validity arise when the specific experimental conditions do not realistically take into account the interactions of other relevant variables in the real world.