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