Reliability and Validity

Citation: Huitt, W. (1999, October). Reliability and validity. Educational Psychology Interactive. Valdosta, GA: Valdosta State University. Retrieved [date], from

The collecting of quantitative data (measurement) and doing research always raises the issues of reliability and validity. The issue of reliability is essentially the same for both measurement and research design. Reliability attempts to answer our concerns about the consistency of the information collected (i.e., can we depend on the data or findings?), while validity focuses on accuracy. The relationship between reliability and validity can be confusing because measurements (e.g., tests) and research can be reliable without being valid, but they cannot be valid unless they are reliable. This simply means that for a test or study to be valid it must consistently (reliability) do what it purports to do (validity). For a measurement (e.g., a test score) to be judged reliable it should produce a consistent score; for the research study to be considered reliable each time it is replicated it too should produce similar results.

Dictionary definitions of terms used in measurement often give one only part of the picture. For example, validity is given as the adverb of valid which means "strong." Unfortunately, this type of definition is not specific enough when the term is used in certain contexts such as testing or research. Additionally, education and psychology use validity in multiple ways, each having several subvarieties.

In the area of testing (including standardized and teacher made tests), educators and psychologists are concerned with content, criterion-related (predictive), and construct validity. Disciplines that conduct research are concerned with other types of validity: Internal and external. The issues of research validity are discussed from a general perspective by  Campbell and Stanley (1966).


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