1. Measurement Reliability and Validity
Dr. Michael R. Hyman, NMSU

2. Sources of Measurement Differences
M = A + E
where: M = measurement
A = accuracy
E = error: random or systematic

4. Reliability
The degree to which measures are free from random error and therefore yield consistent results

6. Rulers are Reliable and Valid

7. 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

8. The ability of a scale to measure what was intended to be measured
Validity
The ability of a scale to measure what was intended to be measured

10. Validity versus Reliability

12. Scale Evaluation

15. Sensitivity
Measurement instrument’s ability to accurately measure variability in stimuli or responses