Patient-Reported Outcome Measures: The Basics of Psychometrics
Patient-Reported Outcomes Measures (or PROMs) are patient perspective questionnaires given before and after an elective procedure and can be extremely useful for statistical analysis of patient care. These questions use psychometrics to collect data on the effectiveness and quality of care given to NHS patients. Psychometrics is the theory and technique of psychological measurements and statistics. The psychometric properties of the questionnaires concern the level of measurement, reliability, validity and responsiveness of the questions themselves as posed to the patients. Psychometrics also considers the construction of the assessment protocol regarding the questionnaire as a whole.
Levels of measurement within psychometrics involve the basic facts of the patient and are broken down into four levels of data:
Nominal – nominal level of data generally breaks down into equal categories. Using a hypothetical patient as an example, nominal data could describe whether a patient’s hip replacement is for the left or right joint, or both.
Ordinal – ordinal level data also uses categories, although they do not have to have equal intervals. In our hypothetical patient’s case, ordinal might refer to whether she is currently walking with a cane, walker or is wheelchair restricted.
Interval – interval levels of data refer to equal aspects of measurement without a true zero such as our patient’s temperature or age (as a zero does not stipulate the lack of temperature or time of life).
Ratio – ratio data levels have equal intervals between measurements and encompass a true zero. Our patient’s pulse, in this case, should it fall to zero, would mean more than a hip replacement is immediately required.
Reliability in psychometrics is essential if you plan on making decisions on the outcome of your data. In PROMs, the outcome is performance based, thus the participation of the patient is required. This involves a Test-Retest reliability. Our patient is given a questionnaire a few days before her hip replacement and again three to six months after to rate the change in her quality of life post-procedure. The differences to both questionnaires are then evaluated to determine if the procedure’s outcome was favorable or not.
Validity, in the case of PROMs, is based on how well the questionnaire measures the patient’s quality of care and can only be determined in relation to a particular question to a given population – patients with a hip replacement, in this case.
The responsiveness of a PROM is its ability to detect change when it has occurred. This happens both externally and internally:
External responsiveness compares how dramatic (or not) the physical changes are before and after the procedure. Can our patient now walk without the aid of a cane?
Internal responsiveness is how we measure change between the first questionnaire and the second. When our patient rates her overall health on a scale of zero to one hundred, is the second score better than the first?
PROMs, when used effectively, are vital tools in health care. However, to use these tools effectively, their psychometric properties should be taken into account to determine which outcomes are relevant to the patient’s quality of care and quality of life.