Tests wherein the purpose is clear, even to naïve respondents, are said to have high face validity. This is the least sophisticated measure of validity.
There are two main categories of validity used to assess the validity of the test (i.e., questionnaire, interview, IQ test, etc.): Content and criterion.įace validity is simply whether the test appears (at face value) to measure what it claims to. Internal validity can be improved by controlling extraneous variables, using standardized instructions, counterbalancing, and eliminating demand characteristics and investigator effects.Įxternal validity refers to the extent to which the results of a study can be generalized to other settings (ecological validity), other people (population validity), and over time (historical validity).Įxternal validity can be improved by setting experiments in a more natural setting and using random sampling to select participants. In other words, there is a causal relationship between the independent and dependent variables. Internal validity refers to whether the effects observed in a study are due to the manipulation of the independent variable and not some other factor. If such a ruler existed it would be an interesting conversation piece, but as a measuring instrument it would be a miserable failure.Internal and External Validity In Research Before you decide that your imaginary uncle is a tightwad, I should tell you that the ruler is made of an extremely rare wood with an interesting property – the wood shrinks and expands randomly – not according to humidity or temperature or day of the week, but randomly. Imagine that you have a rich uncle who has just returned from a cruise to an exotic country, and he has brought you as a souvenir a small ruler – not a pygmy king, but a piece of wood with markings on it. These two properties, reliability and validity, are the focus of this chapter.
The major focus is on a logical understanding of the concepts, as well as an applied understanding through the use of various statistical approaches.Įvery measuring instrument, whether it is a yard-stick or an inventory of depression, must have two properties: the instrument must yield consistent measurement, i.e., must be reliable, and the instrument must in fact measure the variable it is said to measure, i.e., must be valid.
These two properties are defined and the various subtypes of each discussed.
AIM This chapter introduces the concepts of reliability and of validity as the two basic properties that every measuring instrument must have.
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