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Table 2 Summary of results of Rasch analysis: original and revised subscales during pregnancy and postpartum

From: Measuring physical and mental health during pregnancy and postpartum in an Australian childbearing population - validation of the PROMIS Global Short Form

Subscale

Analysis

Item No.

Overall model fit

Item fit residual

mean (SD)

Person fit residual

mean (SD)

PSI

Cronbach alpha

% sig

t-testsa

Pregnancy (Baseline)

 Original Mental health (4 items)

1

2, 4, 5, 10

Chi sq. = 14.21 df = 16, p = .58

.12 (2.35)

−.44 (1.22)

.79

.83

5.24%

(CI: 2.8–7.8)

 Revised Mental Health (remove item 10)

2

2, 4, 5

Chi sq. = 11.79, df = 9, p = .22

−.01 (1.12)

−.52 (1.01)

.77

.84

3.65%

 Revised Mental Health (add item 9)

3

2, 4, 5, 9

Chi sq. = 8.45, df = 16, p = .93

−.21 (.82)

−.63 (1.27)

.84

.88

5.4%

(CI: 2.8–8.0)

 Original Physical Health (4 items)

4

3, 6, 7, 8

Chi sq. = 19.03, df = 16, p = .27

−.09 (1.06)

−.37 (.99)

.64

.69

2.63%

 Revised Physical Health (add item 1)

5

1, 3, 6, 7, 8

Chi sq. = 29.14, df = 20, p = .08

−.12 (1.45)

−.39 (1.09)

.74

.76

3.62%

Postpartum (26-weeks)

 Revised Mental Health

6

2, 4, 5, 9

Chi sq. = 13.86, df = 12, p = .31

−.18 (1.0)

−.48 (1.01)

.84

.87

3.65%

 Revised Physical Health

7

1, 3, 6, 7, 8

Chi sq. = 34.82, df = 15, p = 0.02

−.62 (2.08)

−.42 (.88)

.72

.75

5.6%

(CI: 2.8–8.4)

  1. Chi sq chi-square, df degrees of freedom, p probability, PSI person separation index, CI confidence interval
  2. aConfidence interval only reported if the % value exceeds 5%