PRACTICAL APPLICATIONS

Looking at a symptom-based outcome measure for asthma

A symptom-based outcome measure for asthma has been developed that is more responsive to change than generic measures; this reinforces support for disease-specific outcome measures, say UK investigators.

They developed a lO-item, symptom-based outcome questionnaire that physicians could use to evaluate the quality of care within primary and ambulatory care settings [see box]. The question­naire was administered to 597 patients with asthma; the overall response rate was 93%.

Items in the asthma outcome measure

Asthma symptoms

Breathlessness during exercise

Breathlessness during day ...men not exercising

Wheezing during day Coughing during day Wheezing at night

Breathlessness at night

Coughing al night Disturbed sleep

Fear because of asthma

Feeling of tightness in chest • Used in 5-item scale 1 Of 2

Inclusion in reduced scale"

1 and 2 2 only

1 only 1 only 2 only

Not used 1 and 2

Not used

1 only

2 only

'Rules' for developing outcome measures The development of an outcome measure requires

adherence to specific 'rules', say the investigators. Considerable time and effort can be saved by reviewing the literature to determine whether outcomes measures have already been developed in the field of interest. They add that if additional symptom-based measures need to be included in a new questionnaire, their reliability and validity must be consistent with existing outcome measures.

Importantly, in order to evaluate the impact of healthcare, an outcome measure must be responsive and sensitive to change. The asthma symptom question­naire was administered to 250 patients twice over a 3-month period. During this time there was 'reasonable agreement' between patients' assessment of change in health status and actual change in asthma symptom scores.

Evaluating different questionnaire forms A preliminary analysis of the performance of

different forms of the questionnaire was based on 26 patients who reported marked improvement in their asthma over time. Between baseline and follow-up, there was a significant decrease in the mean total symptom score for all forms of the questionnaire [see table]. Scores using the unweighted symptoms scale were similar to those for the weighted scale and both 5-item scales performed as well as the lO-item scale [see box]. Thus, there appeared to be no advantage in weighting different symptoms, and reducing the scale to 5 items appeared to have no

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detrimental impact on performance, the investigators point out.

Table: Change in mean total asthma symptom score

Queat!onn.Jre Baseline Follow-up

Unwelghted 14.5 8.5 symptom scale

Weighted symptom 14.9 9.7 scale

Reduced scale 1 8.1 4.9

Reduced scale 2 8.1 4.7

SF-36' 58.9 55.8

• 13126 patients completed 11118 questlonnalre

Interestingly, there was no change in health status between baseline and follow-up as measured by the generic quality-of-life measure SF-36. 'Thus there is some preliminary evidence to suggest that, for asthma at least, the symptom based outcome measure is much more sensitive to change in a patient's asthma than is a generic measure of general health perception "

Steen N, Hutchinson A, McColl E, Eccles MP, Hewison J, et a1. Development of a symptom based outcome measure for asthma. British Medical Joumal309: 1065-1068,22 Oct 1994 800313070

PHARMACORESOURCES 5 Nov 1994

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