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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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