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Table 3 Item reduction results based on the IRT

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

Item No. Step 1. EFA Step 2. IRT
Factor 1 Factor 2 Discrimination Item information functionb
Factor loading< 0.3a < 1a < 0.5a
1 0.356 0.421c 2.830 > 2, < 2.5
2 0.313 0.405c 2.848 > 2, < 2.5
3 0.342 0.407c 3.496 > 3, < 3.5
4 0.357 0.368c 1.987 > 1, < 1.5
5 0.361c 0.248 0.778 < 0.2
6 0.506c 0.115 1.097 < 0.4
7 0.274 0.181 Removed
8 0.369c 0.258 0.769 < 0.2
9 0.427c 0.203 1.024 < 0.3
10 0.343c 0.153 0.768 < 0.2
11 0.470c 0.160 1.211 < 0.5
12 0.365c 0.184 0.854 < 0.3
13 0.373c 0.171 0.884 < 0.3
14 0.466c 0.218 1.147 < 0.4
15 0.544c 0.207 1.485 > 0.6, < 0.7
16 0.544c 0.045 1.328 > 0.5, < 0.6
17 0.456c −0.128 1.237 < 0.5
18 0.368c 0.077 0.801 < 0.2
19 0.494c 0.186 1.178 < 0.5
20 0.592c 0.031 1.567 < 0.5
21 0.394c 0.205 0.850 < 0.3
22 0.491c −0.063 1.506 > 0.6, < 0.7
23 0.220 −0.023 Removed
24 0.352c 0.068 0.793 < 0.2
25 0.404c −0.076 0.991 < 0.3
26 0.262 −0.150 Removed
27 0.485c −0.052 1.429 > 0.6, < 0.7
28 0.519c −0.041 1.517 > 0.7, < 0.8
29 0.173 −0.059 Removed
30 0.575c −0.087 1.666 > 0.8, < 0.9
31 0.212 −0.017 Removed
32 0.346c −0.242 0.998 < 0.3
33 0.345c 0.042 0.762 < 0.2
34 0.271 −0.060 Removed
35 0.214 −0.197 Removed
36 0.383c −0.351 1.068 < 0.4
37 0.449c −0.162 1.099 < 0.4
38 0.410 −0.514c 0.321 around 0
39 0.403 −0.441c 0.303 around 0
40 0.330 −0.461c 0.360 around 0
41 0.372 −0.510c 0.289 around 0
42 0.433c −0.182 1.224 < 0.5
43 0.526c −0.089 1.357 > 0.5, < 0.6
44 0.450c −0.180 1.306 > 0.5, < 0.6
45 0.479c 0.021 1.048 < 0.4
46 0.465c −0.280 1.515 > 0.7, < 0.8
  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. bHighest point on the item information function curve;
  5. cindicates which factor the item belongs to base on the EFA
  6. IRT Item response theory, EFA Exploratory factor analysis