Measurement invariance analysis of the Postpartum Specific Anxiety Scale - Research Short Form in mothers of premature and term infants.

Whilst the PSAS-RSF achieved configural invariance and so retains its four-factor structure, metric invariance was not reached and so items are being interpreted differently in mothers of premature infants. Items concerning infant-separation, finance, and anxieties surrounding infant health are potentially problematic. Future research must now modify the PSAS-RSF for specific use in mothers of premature infants, to ensure measurement of anxiety in this population is valid.