The minimal clinically important difference determined using item response theory models: an attempt to solve the issue of the association with baseline score.
OBJECTIVES
Determining the minimal clinically important difference (MCID) of questionnaires on an interval scale, the trait level (TL) scale, using item response theory (IRT) models could overcome its association with baseline severity. The aim of this study was to compare the sensitivity (Se), specificity (Sp), and predictive values (PVs) of the MCID determined on the score scale (MCID-Sc) or the TL scale (MCID-TL).


STUDY DESIGN AND SETTING
The MCID-Sc and MCID-TL of the MOS-SF36 general health subscale were determined for deterioration and improvement on a cohort of 1,170 patients using an anchor-based method and a partial credit model. The Se, Sp, and PV were calculated using the global rating of change (the anchor) as the gold standard test.


RESULTS
The MCID-Sc magnitude was smaller for improvement (1.58 points) than for deterioration (-7.91 points). The Se, Sp, and PV were similar for MCID-Sc and MCID-TL in both cases. However, if the MCID was defined on the score scale as a function of a range of baseline scores, its Se, Sp, and PV were consistently higher.


CONCLUSION
This study reinforces the recommendations concerning the use of an MCID-Sc defined as a function of a range of baseline scores.
['Rouquette|Alexandra|A|', 'Blanchin|Myriam|M|', 'Sébille|Véronique|V|', 'Guillemin|Francis|F|', 'Côté|Sylvana M|SM|', 'Falissard|Bruno|B|', 'Hardouin|Jean-Benoit|JB|']
D000368:Aged D006801:Humans D008962:Models, Theoretical D017063:Outcome Assessment, Health Care D057566:Self Report D012720:Severity of Illness Index D011795:Surveys and Questionnaires
Minimal clinically important difference Item response theory Questionnaires Patient-reported outcomes Rasch models Sensitivity and specificity