Skip to main content

Table 1 Psychometric properties definitions in the field of health-related assessment

From: Sample size used to validate a scale: a review of publications on newly-developed patient reported outcomes measures

Properties

Definitions

Content validity

The ability of an instrument to reflect the domain of interest and the conceptual definition of a construct. In order to claim content validity, there is no formal statistical testing, but item generation process should include a review of published data and literature, interviews from targeted patients and an expert panel to approach item relevance [2].

Face validity

The ability of an instrument to be understandable and relevant for the targeted population. It concerns the critical review of an instrument after it has been constructed and generally includes a pilot testing [2].

Construct validity

The ability of an instrument to measure the construct that it was designed to measure. A hypothetical model has to be formed, the constructs to be assessed have to be described and their relationships have to be postulated. If the results confirm prior expectations about the constructs, the instrument may be valid [2].

Convergent validity

Involves that items of a subscale correlate higher than a threshold with each other, or with the total sum-score of their own subscale [2].

Divergent validity

Involves that items within any one subscale should not correlate too highly with external items or with the total sum-score of another subscale [2].

Known group validity

The ability of an instrument to be sensitive to differences between groups of patients that may be anticipated to score differently in the predicted direction [2].

Criterion validity

The assessment of an instrument against the true value, or a standard accepted as the true value. It can be divided into concurrent validity and predictive validity [2].

Concurrent validity

The association of an instrument with accepted standards [2].

Predictive validity

The ability of an instrument to predict future health status or test results. Future health status is considered as a better indicator than the true value or a standard [2].

Reliability

Determining that a measurement yields reproducible and consistent results [2].

Internal consistency

The ability of an instrument to have interrelated items [2].

Repeatability

(Test-retest reliability) The ability of the scores of an instrument to be reproducible if it is used on the same patient while the patient’s condition has not changed (measurements repeated over time) [2]. Measurement error is the systematic and random error of a patient’s score that is not attributed to true changes in the construct to be measured [17].

Responsiveness

The ability of an instrument to detect change when a patient’s health status improves or deteriorates [2].