Measurement

1
Measurement

• Cameron G. Thies
• University of Iowa

2
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

3
Conceptualization

• The process of formulating and clarifying
  concepts
• Refer to the existing literature
• Keep in mind that many concepts are
  multidimensional
• Examples

4
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

5
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

6
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

7
Validity

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

8
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

9
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