A within-patient change in
pain score
after treatment is statistically 'reliable' when it exceeds the smallest detectable difference (SDD). The aims of the present study were to: (i) determine
SDDs for VAS-scores of
pain intensity, for sufficiently long test-retest intervals to include most
biological fluctuations, (ii) examine whether SDD is invariant to baseline score, and (iii) discuss the value of reliable change (RC) for detecting clinically important difference (CID) or as a possible
indicator of successful treatment.
SDDs were determined using duplicate data from 118 patients with myogenous
Temporomandibular disorders: (1) VAS-scores of
pain intensity from the masticatory system in a pre-treatment diary, and (2) VAS-scores of
pain intensity from the hand (cold-pressor test). RC was determined in VAS-scores from a pre- and post-treatment questionnaire. The long-term SDD was 49mm. A regression analysis on duplicate VAS-scores showed that SDD was largely invariant to the baseline level. Because RC (change>SDD) exceeded CID, it might serve as an
indicator of successful treatment. However, only 17% of the patients showed RC
after treatment, mainly because the baseline was smaller than SDD in 67% of the patients thus making detection of any treatment effect impossible. For patients with possible detection (33%), the frequency of RC was 51%. If the detection threshold would be avoided by provoking
pain in patients with a low baseline, a long-term RC in VAS-scores might occur in about half of all myogenous TMD patients and might then serve as an
indicator of cases of treatment success.