Construction of a global assessment scale of family function, using a questionnaire

Self-report questionnaires are commonly used in family research, but very little attention is paid to the specific measurement properties of the ordered categorical data recorded. The item responses of self-report questionnaires consist of ordered categories. The main property of this type of data is that the labels do not represent a mathematical value but only an order, i.e., one set of labels can be replaced by another set of increasing numbers of symbols. The non-additivity of categorical data means that sum scores cannot be used as a global assessment of the variable. The aims of this study were to further develop the third version of the self-report questionnaire Family Adaptability and Cohesion, Evaluation Scales (FACES), for use in Sweden and to construct a global scale of family function for the variables cohesion and adaptability. The statistical methods used take account of the rank-invariant properties of ordered categorical data.