Measurement Validity and Reliability

Reliability:

The degree to which measures are free from random error and

therefore yield consistent results

Validity:

The ability of a scale to measure what was intended to be

measured

Rulers are Reliable and Valid

Sources of Measurement Differences

M = A + E

where: M = measurement

A = accuracy

E = error: random or systematic

• 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

Reliability

TE S T R E TE S T

S TA B IL ITY

E Q U IV A L E N T F O R M S S P L ITTIN G H A L V E S

IN TE R N A L C O N S IS TE N C Y

R E L IA B IL ITY

Validity

F A C E O R C O N TE N T

C O N C U R R E N T P R E D IC TIV E

C R ITE R IO N V A L ID ITY C O N S TR U C T V A L ID ITY

V a lid ity

Sensitivity

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