... contributed to the design of the explanatory model and the study, data collection and analysis, and writing of the manuscript. ML contributed to the design of the study,data analysis and writing of the ... degree of difficulty and level of impor-tance attached to these.• Perception of the performance of usual activities hasan effect upon ratings of general health status and overall condition of ... type of pre-determined items which form the majority of stand-ardised questionnaires, and which may contain elements of little importance to some, whilst omitting items of rel-evance to others....