Evaluating the Longitudinal Item and Category Stability of the SF-36 Full and Summary Scales Using Rasch Analysis
Table 3
SF-36 total scale Rasch analysis summary Item and Person Infit and Outfit statistics for six waves of data collection.
Wave 1
Wave 2
Wave 3
Wave 4
Wave 5
Wave 6
Persons
Mean
-.69
-.68
-.72
-.75
-.80
-.85
S.D.
.24
.22
.24
.23
.23
.24
MAX
.82
.29
.64
.67
.03
.15
MIN
-4.33
-2.70
-2.60
-2.59
-2.54
-2.76
Infit-MNSQ
1.03
1.02
1.03
1.04
1.04
1.03
Infit-ZSTD
-.30
-.40
-.30
-.20
-.20
-.10
Outfit-MNSQ
1.01
1.01
1.00
1.00
.99
.99
Outfit-ZSTD
-.40
-.40
-.30
-.30
-.30
-.20
Person separation
.8
.6
.7
.7
.7
.7
Person reliability
.4
.2
.3
.3
.3
.3
Items
Mean
.00
.00
.00
.00
.00
.00
S.D.
1.11
1.19
1.20
1.21
1.22
1.26
MAX
1.94
1.96
2.05
2.08
2.09
2.31
MIN
-2.64
-2.92
-2.98
-3.01
-2.86
-2.89
Infit-MNSQ
.98
.99
.98
.98
.98
.99
Infit-ZSTD
-2.30
-2.30
-2.20
-1.90
-1.40
-.90
Outfit-MNSQ
.99
1.00
.98
.98
.98
.98
Outfit-ZSTD
-2.30
-2.30
-2.30
-2.00
-1.50
-1.10
Item separation
93.40
89.72
82.81
76.45
67.43
58.09
Item reliability
1.00
1.00
1.00
1.00
1.00
1.00
Notes. Person or item reliability <0.8; Item separation <3.0; Person separation <2.0; values in italic for Infit or Outfit MnSq > 1.34; values underlined for Infit or Outfit MnSq < 0.64.
