Chapter 2 · Survey: Measurement and Scaling · Slide 74/274

Reliability and Validity

Indicates how reliably a measurement instrument measures — i.e. how consistent the results are across repeated measurements.

2.5 · Reliability and Validity Two quality criteria of measurement

Reliability

Dependability

Indicates how reliably a measurement instrument measures — i.e. how consistent the results are across repeated measurements.

No random error: X_R ⟶ 0 ⟹ X_O ⟶ X_T + X_S

The measure is Cronbach's alpha (0 ≤ α ≤ 1)

Values of α ≥ 0.7 are considered acceptable

X_O = X_T + X_S + X_R

Validity

Accuracy

Indicates to what extent a measurement instrument actually measures the matter it is meant to measure.

That is: to what extent measured differences correspond to actual differences between the objects (quality of the measurement).

No measurement error: X_S ⟶ 0, X_R ⟶ 0 ⟹ X_O ⟶ X_T

X_O = X_T + X_S + X_R

QUESTIONSTAR · Dr. Paul Marx 74 / 274