This issue will be very useful for those who would like to know more about measurement scales, and how they are developed and tested. I was pleased to be asked to write the commentary, partly because I use scales a great deal in my research and have an interest in their development, but more importantly because measurement scales are part of a process that is a central feature of nursing. Nurses carry out assessment all the time and in every corner of the profession. This may take the form of description, such as when forming clinical impressions of people using tacit and experiential knowledge, or it may be in the form of measurement, such as when using a scale to derive a score that rates some characteristic or state, for example health status, quality of life, or pressure ulcer risk.