The influence of study population and definition of improvement on the smallest detectable change and the minimal important change of the neck disability index

Abstract

BackgroundReported values of the minimal important change (MIC) and the smallest detectable change (SDC) for the neck disability index (NDI) differ strongly, raising questions about the generalizability of these parameters. The SDC and the MIC are possibly influenced by the study design or by the study population. We studied the influence of the type of anchor, the definition of improvement and population characteristics on the SDC and the MIC of the NDI.MethodsA cohort study including 101 patients with non-specific, chronic neck pain. SDC and MIC were calculated using two types of external anchors. For each anchor we applied two different definitions to dichotomize the population into improved and unimproved patients. The influence of patient characteristics was assessed in relevant subgroups: patients with or without radiating pain and patients with different baseline scores.ResultsThe influence of different anchors and different definitions of improvement on estimates of the SDC and the MIC was only minimal. The SDC and the MIC were similar for subgroups of patients with or without radiation, but differed strongly for subgroups of patients with higher or lower baseline scores.ConclusionsOur study shows that estimates of the SDC and the MIC of the NDI can be influenced by population characteristics. It is concluded that we cannot adopt a single change score to define relevant change by combining the result of previous studies.

Within‐Session and Between‐Session Reliability, Construct Validity, and Comparison Between Individuals With and Without Neck Pain of Four Neck Muscle Tests

“…Regarding dynamometry, previous studies report ICCs of 0.85 or greater [21,42]. ICC values for the NDI are similar to those reported in the literature, but the MDC is lower [43,44], what could be related to the low mean scores for the NDI in the present study. ICCs for the TSK were greater than those found in a previous study (ICC = 0.69) [45].…”

Responsiveness and minimal important change for the ProFitMap-neck questionnaire and the Neck Disability Index in women with neck–shoulder pain

“…One explanation for this may be the low mean NDI baseline scores of 28 and 23 NDI% in sample I and II, respectively. Association between NDI baseline scores and MIC was recently demonstrated, showing larger MIC for those above (i.e., with higher disability) compared to those below (i.e., with lower disability) median baseline score [42, 44, 52]. The same effect of baseline values on MIC in neck pain patients was also shown for pain intensity numerical rating scale [53], but not for Neck Pain Disability Scale [42].…”

“…However, pain frequency may still be important to measure in chronic pain clinical trials since temporal aspects of pain have shown to be a valid dimension discerned from pain intensity, therefore recommended as an outcome [31]. The MICs obtained for NDI are rather low compared with previous studies in chronic neck pain, showing a range of 5–19 % [30, 34, 36, 40–42, 44, 47, 52]. One explanation for this may be the low mean NDI baseline scores of 28 and 23 NDI% in sample I and II, respectively.…”

“…The same situation applies to our result on the MIC for NDI, i.e., they were smaller than minimal detectable change observed in most other studies. As a matter of fact, MIC was always smaller than minimal detectable change in NDI (see compilation, Table 1 in [52]), meaning that MIC may be confounded with measurement error [58]. Thus, using minimal detectable change instead of MIC as cut-off in NDI and ProFitMap-neck increases the certainty of that measurement error will be exceeded and should therefore be the choice when a high rate false positive (low specificity) should be avoided.…”

Reliability and Responsiveness of the Observable Movement Quality Scale for Children with Mild to Moderate Motor Impairments

“…Furthermore, we used a 7-point transition question, focusing on change in movement quality, as recommended (Lauridsen et al, 2007). However, when scoring a GPE, patients are known to have difficulty taking their baseline status into account; as such, GPE ratings are strongly influenced by patients' current health status (de Vet et al, 2015(de Vet et al, , 2007Grøvle et al, 2014;Kamper et al, 2010;Schuller, Ostelo, Janssen, & de Vet, 2014). Moreover, the MIC depends significantly on the anchor's definition of important change (de Vet et al, 2007).…”