Table 2 Model selection: Parkinson disease only: PD-On-Group and PD-Off- Group

PD1

Six factors based on component solutions -no constraints across groups; correlated residuals Facial and Speech

BASELINE MODEL with 95% confidence interval of RMSEA: 0.065 – 0.077

PD2

As PD1: Within a factor all loadings equal

Outside interval. PD2; too simple

PD3

As PD1: Loadings PD-On = Loadings PD-Off

Simpler model than PD2

PD4

As PD3: Also equal factor covariance matrices

Preferred model: Very simple; easy interpretation;

PD5

As PD4: Also residual variances and residual covariances equal across groups

Rejected: Oversimplification