Table 2 Criteria used to appraise classification systems (adapted from Buchbinder et al. [19])

Purpose

Is the purpose, population and setting clearly specified?

Content validity

Is the domain and all specific exclusions from the domain clearly specified?

Are all relevant categories included?

Is the breakdown of categories appropriate, considering the purpose?

Are the categories mutually exclusive?

Was the method of development appropriate?

If multiaxial, are criteria of content validity satisfied for each additional axis?

Face validity

Is the nomenclature used to label the categories satisfactory?

Are the terms used based upon empirical (directly observable) evidence?

Are the criteria for determining inclusion into each category clearly specified?

If yes do these criteria appear reasonable?

Have the criteria been demonstrated to have reliability or validity?

Are the definitions of criteria clearly specified?

If multiaxial are criteria of face validity satisfied for each additional axis?

Feasibility

Is the classification simple to understand?

Is classification easy to perform?

Does it rely on clinical examination alone?

Are special skills, tools and/or training required?

How long does it take to perform?

Construct validity

Does it discriminate between entities that are thought to be different in a way appropriate for the purpose?

Does it perform satisfactorily when compared to other classification systems which classify the same domain?

Reliability

Does the classification system provide consistent results when classifying the same conditions?

Is the intraobserver and interobserver reliability satisfactory?

Generalisability

Has it been used in other studies and/or settings?