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Table 2 Item reduction results based on the CTT

From: Item reduction and validation of the Chinese version of diabetes quality-of-life measure (DQOL)

Item No. Step 1. Item level tests Step 2. EFA Step 3. Internal consistency reliability
Missing rate (%) Mean score SD Factor 1 Factor 2 Item-total corrected correlation coefficientb Cronbach’s alphab
Missing rate > 5%a < 1.8 or > 4.2a < 0.67a Factor loading < 0.3a r < 0.3a Increased after removea (Factor 1: 0.884 Factor 2: 0.822)
1 0.312 2.081 0.711 0.384 0.528c 0.667 0.764
2 0.277 2.132 0.693 0.337 0.519c 0.648 0.772
3 0.243 2.078 0.649 0.357 0.550c 0.695 0.751
4 0.104 2.174 0.725 0.388 0.448c 0.564 0.811
5 0.104 2.653 0.926 0.394c 0.172 0.348 0.882
6 0.069 3.129 0.994 0.518c 0.015 0.492 0.879
7 0.069 2.563 0.811 0.297 0.170 Removed
8 0.035 2.740 1.090 0.398c 0.133 0.367 0.882
9 0.139 2.112 0.679 0.420c 0.262 0.360 0.882
10 14.969 2.449 0.769 Removed
11 0.485 2.161 0.692 0.485c 0.234 0.419 0.880
12 0.035 2.594 0.912 0.406c 0.106 0.361 0.882
13 0.312 2.419 0.900 0.398c 0.171 0.345 0.882
14 0.277 2.290 0.748 0.492c 0.236 0.434 0.880
15 0.035 2.158 0.656 0.566c 0.266 0.498 0.879
16 0.139 2.466 1.201 0.557c −0.137 0.539 0.878
17 0.069 1.727 0.953 0.431c − 0.166 0.415 0.881
18 0.035 2.321 1.072 0.381c −0.068 0.379 0.882
19 0.035 2.556 1.075 0.534c −0.018 0.520 0.879
20 0.069 2.580 1.223 0.608c −0.165 0.597 0.877
21 0.035 2.631 1.225 0.423c 0.060 0.396 0.882
22 0.069 1.724 0.892 0.492c −0.124 0.468 0.880
23 0.035 2.729 1.135 0.230 0.006 Removed
24 0.035 2.960 1.239 0.381c −0.132 0.381 0.882
25 14.414 1.875 0.968 Removed
26 1.802 1.581 0.961 0.245 −0.173 Removed
27 0.416 1.790 1.012 0.487c −0.144 0.451 0.880
28 0.104 1.843 1.047 0.514c −0.152 0.490 0.879
29 0.035 2.445 1.176 0.185 −0.228 Removed
30 0.208 1.882 0.977 0.574c −0.192 0.526 0.878
31 0.035 2.343 1.079 0.222 −0.187 Removed
32 0.069 1.297 0.594 Removed
33 0.104 2.499 1.260 0.355c −0.089 0.342 0.883
34 0.035 1.781 0.945 0.234 −0.029 Removed
35 8.073 1.136 0.415 Removed
36 2.495 1.229 0.593 Removed
37 0.728 1.888 1.147 0.429c −0.166 0.420 0.881
38 3.222 1.262 0.685 0.314c −0.177 0.294 0.883
39 2.668 1.311 0.762 0.332c −0.197 0.305 0.883
40 4.089 1.134 0.431 Removed
41 3.915 1.213 0.633 Removed
42 0.312 1.641 1.018 0.424c −0.263 0.414 0.881
43 0.104 1.998 1.151 0.519c −0.264 0.508 0.879
44 0.069 1.551 0.908 0.441c −0.225 0.425 0.881
45 0.104 2.632 1.317 0.502c −0.182 0.487 0.880
46 0.104 1.353 0.720 0.427c −0.250 0.414 0.881
  1. Bold and italic number indicates the item failed the corresponding test
  2. Dashed box indicates the item(s) was removed from the scale
  3. aExclusion criteria
  4. bTotal scores were calculated as the corrected mean score of the factor
  5. cindicates which factor the item belongs to based on the EFA
  6. CTT Classical test theory, EFA Exploratory factor analysis, SD Standard deviation, N/A Not applicable