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. 2010 Sep 3;8:94. doi: 10.1186/1477-7525-8-94

Table 5.

Rasch-based statistics for the different strategies applied to enhance the metric properties of the instruments (n = 243)

Items Strategy 1:
Collapsing response
scale		 Strategy 2:
Deleting misfitting
items		 Strategy 3:
Merging DIF
items		 Strategy 4:
Merging DIF items
(Option 1 or 2)
δ SE τ z p r δ SE τ z p r δ SE τ z p r δ SE τ z p r
SWLS recoding: 0 1 1 2 2 3 4 no DIF in selected option
Overall 0.990 0.87 0.250 0.90 0.000b 0.89
Ideal life 0.48 0.11 ord -0.83 0.811 0.39 0.07 disord -0.88 0.119 0.32 0.06 ord -1.11 0.014
Life conditions 0.077 0.11 ord 0.08 0.910 0.06 0.07 ord -0.43 0.220 0.11 0.06 ord -0.56 0.006b
Life satisfaction -0.56 0.11 ord 0.75 0.870 -0.45 0.07 ord 0.43 0.758 -0.24 0.06 ord 0.07 0.165
Got things I want del del merg
Change nothing in life del del merg
Merged item 4. and 5. -0.19 0.04 ord 2.67a 0.038
LiSAT recoding: 0 1 1 1 2 3 recoding: 0 1 1 1 2 3
Overall 0.074 0.81 0.106 0.80 0.000b 0.86 0.125 0.81
Life as a whole -0.44 0.12 ord -1.72 0.022 del -0.08 0.07 ord -1.96 0.000b -0.35 0.122 ord -1.38 0.037
Self care -0.08 0.10 ord 0.32 0.739 -0.08 0.06 ord 1.69 0.558 0.12 0.05 ord 0.68 0.626 0.00 0.098 ord 0.65 0.671
Vocational situation 0.27 0.10 ord -1.82 0.382 0.10 0.06 disord 0.25 0.125 0.30 0.06 disord -0.55 0.321 0.34 0.105 ord -1.35 0.454
Financial situation 0.12 0.11 ord 0.53 0.305 del merg merg
Leisure situation 0.41 0.11 ord -1.55 0.279 0.18 0.06 ord -1.22 0.014 merg merg
Sexual life 1.39 0.11 ord 1.93 0.055 0.86 0.06 disord 0.50 0.777 0.995 0.06 disord -0.11 0.476 1.45 0.112 ord 2.23 0.049
Partner relations del del -0.27 0.07 disord 2.77a 0.008 del
Family life del del -0.53 0.06 disord 2.74a 0.021 del
Contact with friends -1.67 0.11 ord 1.97 0.517 -1.06 0.07 disord 0.58 0.481 -0.77 0.07 disord 0.15 0.562 -1.63 0.110 ord 2.37 0.427
Merged item 4. and 5. 0.24 0.04 ord -1.66 0.279 0.18 0.078 disord -2.25 0.616
PWI no recoding (one item disordered)
Overall 0.346 0.92 0.710 0.92
Whole life 0.17 0.04 ord 0.26 0.250 0.11 0.04 ord -0.70 0.121
Living standard 0.06 0.04 ord 0.97 0.050 0.00 0.04 ord 1.66 0.427
Health del merg
Life achievement 0.09 0.04 ord 1.28 0.857 0.03 0.04 ord 1.62 0.646
Relationships -0.35 0.04 ord 1.68 0.207 merg
Feeling safe -0.08 0.04 ord -1.04 0.481 merg
Feel part of community -0.06 0.04 disord 0.06 0.598 -0.09 0.041 disord 0.495 0.730
Future security 0.18 0.04 ord -0.46 0.681 merg
Merged item 3. and 8. 0.19 0.03 ord 0.54 0.949
Merged item 5. and 6. -0.23 0.03 ord -1.00 0.501
WHOQOL no recoding (no disorder)
Overall 0.340 0.81 0.567 0.76
Health 0.12 0.10 ord 0.15 0.371 merg
Activities of daily living 0.68 0.09 ord -0.30 0.240 0.58 0.08 ord -0.29 0.604
Relationships del -0.41 0.08 ord 1.59 0.582
Living place del -0.34 0.08 ord 1.92 0.475
Quality of life -0.80 0.10 ord 0.07 0.376 merg
Merged item 1. and 5. 0.16 0.06 ord -2.20 0.208

Index:

a: Exceeds the critical value of z > +/-2.5

b: Below the Bonferroni corrected probability level of p < 0.05/number of items (SWLS and PWI: p < 0.01; LISAT and PWI: p < 0.006)

Abbreviations:

SWLS: Satisfaction with life scale; LISAT: Life satisfaction questionnaire; PWI: Personal well-being index; WHOQoL: World Health Organization quality of life assessment; DIF: Differential item functioning; δ: Item location in logits (delta); SE: Standard error of item location; τ: Ordering of the response scale thresholds (tau); z: Standard normal distributed test value z; p: Probability of the Chi2 test; r: Person reliability index; del: Item deleted due to misfit; merg: Item merged due to DIF; ord: Response scale thresholds ordered; disord: Response scale thresholds disordered