Question

Explain the concepts of internal validity and external validity and give examples. Thanks

Answer 1

Validity is the extent to which an instrument/test measures what it intends to measure.

Internal validity is how well the cause- effect relations found between variables in a study is true or authentic.It only applies to studies that establish causal relationships.It is the measure of how accurate are the results of a study.If the causal relationship has been formed with no control on confounding variables then internal validity is low.However if the causal relationship is caused only by the independent variable, internal validity is high. For example a correlation studying relationship between height and mental ability may find a positive correlation, if it considers school children who grow taller as they age and progress to next grade.So a shorter child may score less on a test than a taller one, but the causal variable is not height, rather the confounding variable of age and grade.Thus the study has a poor internal validity.

External Validity refers to the extent to which results of one study are applicable to other situations or can be generalized to the general population which is the aim of research. For example a test module designed to teach English Language to 6 year olds was found to be highly effective, however when tested in non English speaking regions, the module was ineffective, thus having a low external validity, as its efficiency could not be replicated in a different setting.