Table 8

Factor analysis of the extended version of the baseline PRUNE and contribution to item reduction
Items on baseline longer version of PRUNE (before final item reduction) Subscale Explanation of final decisions on items deleted from the final scale during production processes
Pain Usual activity /role Specific activity Sensory/motor symptoms
Variance Explained by factor (%) 24 15 26 10 Although some items cross loaded as below; the largest amount of variance was by specific activity items; followed by pain, usual activity and sensory/motor symptoms
Pain - At its worst 0.86 0.12 0.26 0.12
Pain - At Rest 0.76 0.21 0.36 0.02
Pain - Morning 0.74 0.28 0.33 0.26
Pain - During activity 0.70 0.29 0.51 0.26 Pain during activity was dropped from the reduced measure
Pain - After activity 0.85 0.15 0.24 0.19
Pain - At night 0.83 0.20 0.25 0.02
Pain - Frequency 0.89 0.19 0.11 0.16
SM - Numbness 0.37 0.74 −0.02 0.24 Hand weakness cross loads but left as a component of sensory/motor symptoms scale given importance. Motor Control item clarified based on respondent feedback
SM - Pins And needles 0.27 0.76 0.18 −0.04
SM - Control finger 0.14 0.78 0.23 0.13
SM - Weakness in hand 0.46 0.47 0.06 0.46
SA - Combing hair 0.32 0.25 0.78 0.29 Hair combing deleted: not applicable to a number of respondents
SA - Eating 0.15 0.40
    0.67
0.30
SA - Lift heavy object 0.34 0.18
    0.72
0.31
SA - Finger task
    0.49
0.04
    0.66
0.37
SA - Pull
    0.43
0.12
    0.39
0
    .52
Pulling deleted due to cross loading and correlation with heavy lifting
SA - Throw a small object 0.32 0.10
    0.81
0.24 Throwing deleted due to higher rate of missingness
SA - Use a telephone 0.39 0.00
    0.73
0.26
SA - Doing up buttons 0.12 0.25
    0.59
0.21 Doing buttons and washing deleted based on cross correlations and interviews
SA - Wash opposite armpit 0.30 0.11
    0.73
0.26
SA - Reaching 0.35 0.01
    0.82
0.15
SA - Turning a doorknob 0.19 0.08
    0.69
0.45
UA - Personal care −0.02 0.06 0.40 0.60
UA - Household 0.11 0.14 0.41 0.68
UA - Work 0.14 0.08 0.27 0.85
UA - Recreational activities 0.22 0.12 0.37 0.77

Principal Component Analysis with Varimax with Kaiser Normalization for items in the longer version of the PRUNE before the final item reductions were completed. Factor loadings are color-coordinated to highlight loading over 0.40. (Pain subscale items in bold, sensory/motor symptoms items in italics, specific activity items in underline (SA) and usual activity items in bolde (UA). Cross loading occurred on a number of items and was one issue considered in the item reduction process (along with the cross correlation between items, and results of patient interviews with respect to item interpretation and clarity).

MacDermid and Grewal

MacDermid and Grewal BMC Musculoskeletal Disorders 2013 14:146   doi:10.1186/1471-2474-14-146

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