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Table 6 Thresholds for the three possible factors of the PHQ-15 based on IRT analysis

From: Validation of the Chinese version of the PHQ-15 in a tertiary hospital

  Diff. Coef. Std. Err. z P > z [95 % Conf. Interval]
Factor 1
 Item 2 1 vs 0 0.351 0.064 5.49 <0.001 0.226 0.477
  2 vs 1 2.094 0.114 18.31 <0.001 1.870 2.318
 Item 3 1 vs 0 0.320 0.065 4.92 <0.001 0.193 0.448
  2 vs 1 1.577 0.095 16.52 <0.001 1.390 1.764
 Item 4 1 vs 0 2.590 0.126 20.50 <0.001 2.342 2.838
  2 vs 1 2.685 0.237 11.32 <0.001 2.220 3.150
 Item 5 1 vs 0 0.792 0.068 11.58 <0.001 0.658 0.926
  2 vs 1 2.567 0.145 17.71 <0.001 2.282 2.851
 Item 6 1 vs 0 0.734 0.068 10.85 <0.001 0.602 0.867
  2 vs 1 2.427 0.136 17.83 <0.001 2.160 2.693
 Item 7 1 vs 0 0.385 0.064 6.09 <0.001 0.261 0.509
  2 vs 1 2.684 0.144 18.61 <0.001 2.401 2.966
 Item 8 1 vs 0 1.910 0.099 19.38 <0.001 1.716 2.103
  2 vs 1 2.277 0.164 13.90 <0.001 1.956 2.598
 Item 11 1 vs 0 1.849 0.096 19.19 <0.001 1.661 2.038
  2 vs 1 2.292 0.162 14.14 <0.001 1.975 2.610
Factor 2
 Item 9 1 vs 0 0.366 0.040 9.16 <0.001 0.288 0.445
  2 vs 1 1.872 0.080 23.43 <0.001 1.715 2.029
 Item 10 1 vs 0 0.558 0.042 13.18 <0.001 0.475 0.641
  2 vs 1 1.641 0.070 23.30 <0.001 1.503 1.779
Factor 3
 Item 1 1 vs 0 0.867 0.063 13.80 <0.001 0.745 0.992
  2 vs 1 2.052 0.112 18.37 <0.001 1.833 2.271
 Item 12 1 vs 0 0.122 0.055 2.21 0.027 0.014 0.230
  2 vs 1 1.737 0.089 19.42 <0.001 1.561 1.912
 Item 13 1 vs 0 0.152 0.055 2.76 0.006 0.044 0.260
  2 vs 1 1.831 0.093 19.67 <0.001 1.649 2.014
 Item 14 1 vs 0 −0.469 0.057 −8.18 <0.001 −0.581 −0.357
  2 vs 1 1.598 0.081 19.64 <0.001 1.439 1.758
 Item 15 1 vs 0 −0.118 0.056 −2.10 0.035 −0.228 0.008
  2 vs 1 1.329 0.075 17.62 <0.001 1.181 1.477
  1. Partial credit model, number of observations = 1329
  2. Factor 1: Log likelihood = −7025.6965; AIC = 14085.390; BIC = 14173.660
  3. Factor 2: Log likelihood = −1942.3235; AIC = 3894.647; BIC = 3920.608
  4. Factor 3: Log likelihood = −5613.5482; AIC = 11249.100; BIC = 11306.210