1. Measurement Validity and Reliability

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

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

8. Rulers are Reliable and Valid

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

11. 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 Causes of Variation in Scale Measurements

13. Reliability

15. Validity

17. Sensitivity A measurement instrument’s ability to accurately measure variability in stimuli or responses.