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Reliability and Validity

The accuracy of our measurements is affected by reliability and validity.  Reliability is the extent to which the repeated use of a measure obtains the same values when no change has occurred (can be evaluated empirically).  Validity is the extent to which the operationalized variable accurately represents the abstract concept it intends to measure (cannot be confirmed empirically-it will always be in question).  Reliability negatively impacts all studies but is very much a part of any methodology/operationalization of concepts.  As an example, reliability can depend on who performs the measurement (i.e., subjective measures) and when, where, and how  data are collected (from whom, written, verbal, time of day, season, current public events).

There are several different conceptualizations of validity.   Predictive validity refers to the ability of an indicator to correctly predict (or correlate with) an outcome  (e.g., GRE and performance in graduate school).  Content validity is the extent to which the indicator reflects the full domain of interest (e.g., past grades only reflect one aspect of student quality).  Construct validity (correlational validity) is the degree to which one measure correlates with other measures of the same abstract concept (e.g., days late or absent from work may correlate with performance ratings).  Face validity evaluates whether the indicator appears to measure the abstract concept (e.g., a person's religious preference is unlikely to be a valid indicator of employee quality). 



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