The MS symptom and impact diary (MSSID): psychometric evaluation of a new instrument to measure the day to day impact of multiple sclerosis; A welcome addition to the toolkit of those who work with multiple sclerosis.(Editorial Commentaries)

It is a truism that multiple sclerosis is not only the most common of the neurodegenerative diseases but also the most variable in presentation and course. This is not only true of the relapsing-remitting form of the disease, where it is particularly evident, but it also applies to the rate of progression within progressive forms of the disorder. These characteristics of the disease pose problems for the clinical management of multiple sclerosis as well as for research into the pathology, treatment, and management of the disorder.

The multiple sclerosis symptom and impact diary (MSSID), reported in this issue, (1) makes a significant addition to the tools available to the researcher and the clinician. The diary is a method by which day to day fluctuations in symptomatology, and their impact on daily life, can be recorded and assessed from the perspective of the patient's own experience. The MSSID has a carefully structured format which contributes to the strength of its psychometric properties, having two questions which address symptoms, five which assess impact, and one open ended question allowing any additional information to be reported. The two questions that inquire about symptoms require, first, a binary decision about the presence of 14 symptom areas "today"; and second a rating of the interference which they produced (although the psychometric analysis indicates that this is treated by respondents as "severity" as well as "impact"). The next five questions require more global five or six point ratings of the impact of the disorder. The practised user can no doubt complete the daily diary entry quickly and easily.

The authors of the MSSID have conducted a thorough and appropriate statistical analysis of the properties of the instrument, which is to be welcomed in a field where such questionnaires are not always so carefully constructed. In their study of 63 outpatient clinic attenders, internal reliability was found to be good, and test-retest reliability acceptable, given that the MSSID retains the ability to record changes which occur on a daily basis. Validity is inevitably a methodologically thorny issue when individual centred instruments are being considered, and in a wholly idiographic questionnaire validity can strictly never be determined. However, the authors demonstrate that the MSSID possesses good discriminant validity, with the expected differences being observed among clinical multiple sclerosis subgroups. Convergent validity is a more questionable approach, but the finding of "moderate" correlations with several cognate measures is what reasonably might be expected.

The relation and differences between the MSSID and other similar measures are what will also determine its usefulness. Before and after the 12 week study, participants also completed an MS-specific measure of quality of life (LMSQoL (2)), a measure of health status (MSQoL-54 (3)), a measure of functional ability (Barthel index (4)), the London handicap scale (LHS (5)), and the reintegration to normal living index (RNLI (6)), the two latter being measures of participation and handicap. None of these is suitable for daily completion, given their length or their likely responsiveness to short term variations in symptoms. The relations between the factors identified in the MSSID and these measures was typically a correlation in the region 0.3 to 0.5, so there is roughly only 10% to 25% of common variance in what is being recorded. This no doubt partly reflects the differing levels of responsiveness of instruments and, more simply, the fact that rather different questions are asked, but it also relates to the individual centred nature of the MSSID and the fact that patients' perceptions of their condition are affected by a range of psychological factors which interact with the "objective" physiological state of the disease. Ample research has shown that individuals' perceptions of their symptoms and the personal impact of their disease are not fully concordant with objectively recorded health status (see, for example, Murrell et al (7) in relation to multiple sclerosis). Neither is more valid than the other; they are related but different phenomena with differing health care implications. It is important to recognise that the MSSID provides an individual based evaluation but gives little valid information to the clinician or researcher about the daily ...