Table 4

SUBGROUPS, person-based hypotheses
Research question Outcome Method of analysis Results from the model data set
All respondents, n = 244 Respondents answering ≥ 80%, n = 161 Respondents answering all first 8 weeks, n = 133
5: Are there subgroups of patients? Subgroups as clusters with low within-cluster variation and high between-cluster variation A. Visual inspection based on plots of the course of pain in a graphical presentation where predefined criteria of directions in early and late phases, a qualitative approach A: Illustrated in Table 5 Not applied Not applied
B: Regression coefficients from spline regression (1 knot) derived from each subject were used in Wards’ hierarchical cluster analysis. Optionally this analysis was followed by K-means cluster analysis. Inspection of number of clusters based on the Calinski-Harabasz criterion and the criteria by Duda & Hart B: Not done due to lack of degrees of freedom in spline regression of some individual subjects B: 4 clusters suggested. Not applied
C: Wards’ hierarchical cluster analysis, optionally followed by K-means cluster analysis, applied directly on the weekly number of pain days for the first 8 weeks. Cluster criteria as in B. Cluster 2: 79 Percentage with short duration in these clusters: C: 6 clusters suggested. Percentage with short duration the previous year in these clusters:
C: Not applied Cluster 1: 39 Cluster 1: 58
Cluster 2: 49 Cluster 3: 20
Cluster 3: 85 Cluster 4: 33
Cluster 4: 37 Cluster 5: 52
C: Not applied Cluster 6: 50

Axén et al.

Axén et al. BMC Medical Research Methodology 2012 12:105   doi:10.1186/1471-2288-12-105

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