Measurement

Cameron G. ThiesUniversity of Iowa

The Measurement Process• What is measurement?– The process of assigning numbers or labels to

units of analysis in order to represent characteristics of those units

– Everyday vs. social science measurement– Examples

• The Measurement Process– We must move from abstract concepts to

concrete manifestations of those concepts– Conceptualization and operationalization

Conceptualization

• The process of formulating and clarifying concepts

• Refer to the existing literature• Keep in mind that many concepts are

multidimensional• Examples

Operationalization• Explaining the procedures that will specify the

value or category of a variable on each case• Also known as creating an operational definition

of a concept• Political scientists develop indicators that match

the case to a category of the variable. An indicator is a single observable measure that acts as an empirical manifestation of a concept.

• Indexes and scales• Examples

Reliability and Validity of Measures

• When we create our operational definitions we must be concerned with both the reliability and the validity of the measures

• Reliability concerns the extent to which a measure yields the same results on repeated trials

• Validity concerns the correspondence between a measure and the concept it is supposed to capture

Reliability• How to assess the reliability of a measure?– test-retest method– alternative-form method– split-halves method– intercoder reliability

• How can we improve the reliability of our measures?– Exploratory studies– Add items to a scale– Item by item analysis– Clear instructions and proper training

Validity

• Assessing validity is more difficult• Types of validity– Face validity– Content validity– Criterion-related validity– Construct validity

Relationship Between Reliability & Validity

• Can a measure be reliable but not valid? Yes.• Can a measure be valid but not reliable? No.– Explain

• How do most researchers deal with issues of reliability and validity?– Rely on measures already used in the existing

literature

Measurement Precision

• Levels of Measurement– Nominal– Ordinal– Interval– Ratio

• Rules for assigning cases to categories– Cases placed in the same category must be

equivalent– Exhaustive and mutually exclusive