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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%