Three ways to quantify uncertainty in individually applied "minimally important change" values.
OBJECTIVE
Determining "minimally important change" (MIC) facilitates the interpretation of change scores on multi-item instruments. This article focuses on how MIC values should be interpreted when applied to individual patients.


METHODS
The MIC value of a hypothetical questionnaire "Q" was determined in a sample of 400 patients who improved and 100 patients who did not improve, using the receiver operating characteristic (ROC) method, and three methods to quantify the uncertainty.


RESULTS
The MIC value on questionnaire Q was 10.5. Firstly, the 95% confidence interval (CI) of the MIC value (for questionnaire Q: 5.6-14.2) quantifies the uncertainty of the estimation of the MIC value. Secondly, "how sure we are that this MIC value holds for every patient" is quantified by the values for sensitivity (74%) and specificity (91%). Thirdly, the smallest detectable change (SDC) on questionnaire Q is calculated (16.0) to consider whether the MIC value (10.5) falls outside or within the measurement error.


CONCLUSIONS
For application in clinical research and practice, MIC values are always considered at the individual level, but determined in groups of patients. The interpretation comes with different forms of uncertainty. To appreciate the uncertainty, knowledge of the underlying distributions of change scores is indispensable.
de Vet
Henrica C W
HC
EMGO Institute for Health and Care Research, VU University Medical Center, 1081 BT Amsterdam, The Netherlands. hcw.devet@vumc.nl
Terluin
Berend
B
Knol
Dirk L
DL
Roorda
Leo D
LD
Mokkink
Lidwine B
LB
Ostelo
Raymond W J G
RW
Hendriks
Erik J M
EJ
Bouter
Lex M
LM
Terwee
Caroline B
CB
D001294:Attitude to Health; D003627:Data Interpretation, Statistical; D006801:Humans; D017116:Low Back Pain / Q000628:therapy; D017060:Patient Satisfaction; D011594:Psychometrics; D011788:Quality of Life; D012372:ROC Curve; D016896:Treatment Outcome; D035501:Uncertainty