Measurement Reliability and Validity

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Measurement Reliability and Validity
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Sources of Measurement Differences M A
E where M measurement A true
indicator E random or
systematic error
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Reliability

• Degree to which measures are free from random
  error and therefore yield consistent results

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Validity

• Ability of a scale to measure what was intended
  to be measured

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Validity versus Reliability
Validity
Reliability
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Rulers are Reliable and Valid
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Causes of Variation in Scale Measurements

• True differences in the characteristic being
  measured
• Differences due to stable characteristics of
  individual respondents
• e.g., intelligence, education
• Differences due to short-term personal factors
• e.g., health, fatigue, motivation
• Differences caused by situational factors
• e.g., rapport with interviewer, distractions
• Differences resulting from variations in
  administering the survey
• e.g., different interviewers
• Differences due to the sampling of items
  included in the questionnaire
• Differences due to a lack of clarity in the
  measurement instrument
• e.g., ambiguity, complexity, interpretation
• Differences due to mechanical or instrument
  factors
• e.g., lack of space to record response,
  appearance of questionnaire
• Differences in scoring/coding responses

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Scale Evaluation
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Approaches to Reliability Assessment

• Test-retest
• Split sample
• Alternative forms
• Internal comparison
• Inter-scorer

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Approaches to Validity Assessment

• Content/face
• Predictive/criterion
• Convergent
• Divergent
• Nomological

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Sensitivity

• Measurement instruments ability to accurately
  measure variability in stimuli or responses