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

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

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

Rulers are Reliable and Valid

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

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

Validity versus Reliability

Scale Evaluation

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