[The complexity of the concept oral health-related quality of life]

The methods uses most often for developing and analyzing questionnaires, such as the explorative factor analysis and Cronbach's alpha, presume that psychological constructs are latent (imperceptible) and that there is a reflective-measurement model with the underlying assumption of local independence. Local independence means that the latent variable explains why the variables observed are related. Many questionnaires for measuring oral health-related quality of life are analyzed as if they were based on a reflective-measurement model assuming local independence. This assumption requires these questionnaires to contain solely items reflecting instead of determining oral health-related quality of life. The tenability of this assumption is questionable.