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Measurement invariance of the SF-12 across European-American, Latina, and African-American postpartum women

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Abstract

Purpose

The purpose of this study was to determine whether a postpartum-specific version of the SF-12 was invariant across three ethnic groups. Specifically, we examined the presence of differential item functioning (DIF) among European-American, Latina, and African-American mothers. DIF refers to differential endorsement of item responses that are not due to the construct being measured. DIF can result in biased group comparisons.

Methods

We analyzed cross-sectional data of postpartum women (n = 655) who delivered at an urban hospital in the northeast region of the USA. Multiple indicators multiple causes (MIMIC) model was used to examine differential item functioning.

Results

The analyses revealed the presence of DIF for three items: Item 1 “self-assessed general health,” item 8 “bodily pain,” and item 9 “calm and peaceful.” Only two DIF effects were meaningful based on odds ratios and on the percentage of the total effect accounted for by the DIF effect. Specifically, African-American women differentially endorsed item 8 “bodily pain” when compared to European-American women (OR = 2.11, CI95 = 1.20, 3.71) and Latinas were more likely to endorse item 9 “calm and peaceful” when compared to European-American women (OR = 2.62, CI95 = 1.64, 4.17).

Conclusion

The results of this study indicate that the SF-12 is to a great degree an invariant measure for the assessment of HRQoL among postpartum ethnically diverse women. More research is needed to examine other aspects of invariance (e.g., configural and metric) and longitudinal invariance in ethnically diverse samples. To better understand ethnic differences in health, future studies need to examine the factors that may underlie DIF effects in quality of life.

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Abbreviations

SF-12:

Short-form health survey

MIMIC:

Multiple indicator multiple causes

DIF:

Differential item functioning

HRQoL:

Health-related quality of life

MOP:

Maternity outcomes project

PCS:

Physical component summary

MCS:

Mental health component summary

SEM:

Structural equation modeling

CFS:

Confirmatory factor analysis

WLSMV:

Weighted least squares mean and variance adjusted estimator

MLR:

Maximum likelihood estimator with robust standard errors estimator

MCAR:

Missing completely at random

OR:

Odds ratio

χ2 :

Chi-square test

CFI:

Comparative fit index

TLI:

Tucker–Lewis index

RMSEA:

Root mean square error of approximation

WRMR:

Weighted root mean square residual

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Acknowledgments

This study was based on the first author’s master’s thesis. This research was supported by Agency for Healthcare Research and Quality (RO1 HS09698-3) and Robert Wood Johnson Foundation Grant (42680).

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Authors and Affiliations

  1. Department of Psychology, The University of Texas at Arlington, 501 S. Nedderman Suite 313, Arlington, TX, 76019, USA

    Tamer F. Desouky & Pablo A. Mora

  2. Department of Obstetrics and Gynecology, Mount Sinai Medical Center, New York, NY, USA

    Elizabeth A. Howell

Authors
  1. Tamer F. Desouky
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  2. Pablo A. Mora
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  3. Elizabeth A. Howell
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Correspondence to Pablo A. Mora.

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Desouky, T.F., Mora, P.A. & Howell, E.A. Measurement invariance of the SF-12 across European-American, Latina, and African-American postpartum women. Qual Life Res 22, 1135–1144 (2013). https://doi.org/10.1007/s11136-012-0232-5

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