ABSTRACT
In each of these examples, it is the concept or surrogate that is measured, not the actual “thing” that we desire to measure.
In the physical and life sciences, we tend to think that the relationship between the unobservable and the observable is a strong one. But the natural question that arises is to what extent does a particular response represent the particular construct or unobservable variable we are interested in. That is the nature of validity-a measurement is valid if it measures what it is supposed to measure. It would make little sense to measure a person’s cholesterol level using a ruler or quantify a person’s IQ using a bathroom weight scale. These are all invalid measuring devices. But, validity is not an all-or-none proposition. It is a matter of degree, with some measuring instruments being more valid than others. The scale used in a doctor’s office is probably more accurate and valid than the bathroom scale used in our home.
