The MDC and MCIC values in the PI-NRS for neck and referred pain were estimated for the follow-up period of 3 months.
The Minimal Detectable Change (MDC) was calculated as 1.96 * √2 * SEM. [8 (link),12 (link)] The standard error of measurement (SEM) was estimated by taking the square root of the within subject variance (consisting of variance between measures plus the residual variance on a two-way ANOVA random effects model) of patients categorized as "unchanged" by external criterion. The 95% confidence interval was calculated using the chi-square distribution [29 ]. The MDC can be interpreted as the magnitude of change below which there is more than a 95% chance that no real change has occurred.
The following methods were used to estimate the MCIC [12 (link)]:
1. Mean Change Score (MCS): Mean change of PI-NRS in patients who scored "2" ("improved") on the external criterion. The changes of scores PI-NRS were calculated by subtracting the final values from the baseline values, so that positive scores correspond to improvement.
2. Optimal cutoff point (ROC): Considering the PI-NRS change as a diagnostic test for discriminating between improved and not improved patients, and the external criterion as a gold standard, a ROC curve was developed describing the performance of changes in the corresponding scale to detect improvement [30 (link)]. The optimal cutoff point was estimated by the point that maximizes the sum of specificity and sensitivity.
Data from all recruited patients (both with and without referred pain) were included in the main analysis, in which MDC and MCIC values for neck pain were calculated. In a subgroup analysis, only patients with referred pain at baseline were included, and MDC and MCIC values for neck and referred pain were calculated.
The effects of baseline scores and chronicity on MDC, MCS and ROC were estimated by defining subgroups. Values were estimated for patients with low baseline scores (lowest tertile) and high baseline scores (highest tertile). Values were also estimated for chronic and subacute patients, with the cut-off point for chronicity established at 90 days [1 (link),30 (link)]. All statistical analyses were performed using SPSS for Windows, version 12.0.
The Minimal Detectable Change (MDC) was calculated as 1.96 * √2 * SEM. [8 (link),12 (link)] The standard error of measurement (SEM) was estimated by taking the square root of the within subject variance (consisting of variance between measures plus the residual variance on a two-way ANOVA random effects model) of patients categorized as "unchanged" by external criterion. The 95% confidence interval was calculated using the chi-square distribution [29 ]. The MDC can be interpreted as the magnitude of change below which there is more than a 95% chance that no real change has occurred.
The following methods were used to estimate the MCIC [12 (link)]:
1. Mean Change Score (MCS): Mean change of PI-NRS in patients who scored "2" ("improved") on the external criterion. The changes of scores PI-NRS were calculated by subtracting the final values from the baseline values, so that positive scores correspond to improvement.
2. Optimal cutoff point (ROC): Considering the PI-NRS change as a diagnostic test for discriminating between improved and not improved patients, and the external criterion as a gold standard, a ROC curve was developed describing the performance of changes in the corresponding scale to detect improvement [30 (link)]. The optimal cutoff point was estimated by the point that maximizes the sum of specificity and sensitivity.
Data from all recruited patients (both with and without referred pain) were included in the main analysis, in which MDC and MCIC values for neck pain were calculated. In a subgroup analysis, only patients with referred pain at baseline were included, and MDC and MCIC values for neck and referred pain were calculated.
The effects of baseline scores and chronicity on MDC, MCS and ROC were estimated by defining subgroups. Values were estimated for patients with low baseline scores (lowest tertile) and high baseline scores (highest tertile). Values were also estimated for chronic and subacute patients, with the cut-off point for chronicity established at 90 days [1 (link),30 (link)]. All statistical analyses were performed using SPSS for Windows, version 12.0.
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