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Table 6 Trend τ of item easiness parameter estimated by linear logistic model with relaxed assumptions for each quality of life dimension

From: Item response theory and factor analysis as a mean to characterize occurrence of response shift in a longitudinal quality of life study in breast cancer patients

Dimension Items T1 → T2_Ra T1 → T3_Rb T3 → T4_Rc
N τ p N τ p N τ p
QLQ-C30           
Physical functioning 1 – 4d 100 -0.02 0.858 139 0.27 0.004 201 -0.84 <0.001
Role functioning 6, 7 84 0.36e 0.011 118 0.71 <0.001 164 -0.60 <0.001
Emotional functioning 21 - 24 180 -0.62 <0.001 208 -0.65 <0.001 196 0.22 <0.001
Cognitive functioning 20, 25 103 -1.15 <0.001 129 -0.29 0.020 130 -0.53 <0.001
Social functioning 26, 27 75 0.07 0.791 101 0.66 <0.001 142 -0.51 <0.001
Fatigue 10, 12, 18 141 -0.19 0.280 160 0.23 0.019 183 -0.99 <0.001
Nausea and vomiting 14, 15 37 -0.60 0.022 65 0.50 0.029 98 -0.36 0.003
Pain 9, 19 96 0.11 0.410 124 0.37 0.001 148 -0.54 <0.001
Dyspnea 8 50 -0.60 0.025 55 -0.30 0.248 94 -0.42 0.014
Insomnia 11 115 -0.49 0.001 135 -0.49 <0.001 147 -0.36 0.005
Appetite loss 13 61 -0.59 0.004 85 -0.14 0.401 90 -0.51 0.003
Constipation 16 71 -0.16 0.392 89 0.17 0.295 93 -0.41 0.009
Diarrhea 17 39 -1.34 <0.001 64 -0.67 0.005 61 -0.09 0.641
Financial difficulties 28 22 0.16 0.630 33 0.25 0.322 47 -0.45 0.053
QLQ-BR23           
Body image 9 - 12 68 0.10 0.489 119 0.83 <0.001 153 -0.66 <0.001
Sexual functioning 14, 15 55 0.06 0.950 71 0.33 0.078 78 0.77 0.010
Sexual enjoyment 16 13 -1.20 0.04 39 -0.43 0.14 33 0.19 0.49
Future perspective 13 122 -0.56 <0.01 135 -0.46 <0.01 144 0.01 0.95
STSE 1 - 4; 6 - 8 55 -0.40 <0.01 61 0.21 0.013 77 -0.74 <0.001
Breast symptoms 20 - 23 114 -0.11 0.07 135 0.36 0.01 190 -0.76 <0.001
Arm symptoms 17 - 19 97 0.64 <0.001 167 0.86 <0.001 156 -0.37 0.001
Hair loss Q5 6 0.22 0.738 16 0.12 0.808 24 -0.33 0.149
  1. aT1 → T2_R: comparison of baseline quality of life assessment and retrospective measure performed after surgery.
  2. bT1 → T3_R: comparison of baseline quality of life assessment and retrospective measure performed three months later.
  3. cT3 → T4_R: comparison of quality of life assessment at three months and retrospective measure performed three months later.
  4. dQ5 was excluded because of the patients’ responses to this item at baseline: all patients chose either category 1 or 2 for this item at baseline, whereas all four categories were represented on retrospective measures.
  5. eτ =0.364: patients significantly chose higher response categories at the retrospective measure of baseline HRQoL performed after surgery.