Measurement invariance of the Positive Gains Scale in families of children with and without disabilities.

Mikeda and colleagues tested whether the Positive Gains Scale (PGS) measures the same thing for mothers of kids with and without developmental delays. They ran a measurement invariance check using confirmatory factor analysis. The sample included mothers from both groups, though exact numbers were not reported.

The PGS showed metric invariance - the basic structure held across groups. But scalar invariance failed. This means you cannot compare raw scores between mothers of kids with versus without disabilities. The scale works differently at the item level for each group.

Koegel et al. (2014) found the exact same pattern with the Autism Spectrum Quotient Short Form - metric but not scalar invariance across ASD and non-ASD groups. This suggests the problem is common across scales, not specific to the PGS.

Cançado et al. (2011) reviewed 16 family quality-of-life instruments and noted the disability field lags behind in rigorous scale development. The PGS invariance failure supports their call for better psychometric work.

Higgins et al. (2021) failed to replicate the 'Down syndrome advantage' for maternal well-being once poverty was controlled. Together with Mikeda's findings, this warns that apparent group differences in parent well-being may be methodological artifacts rather than real effects.

Before you compare PGS scores between parents of kids with and without disabilities, stop. The scale lacks scalar invariance, so any observed differences could be measurement error, not true differences in positive gains. Use the PGS within groups only, or pick a scale with proven invariance. Always check measurement invariance before making group comparisons in your assessments or research.