The low- and higher-order factor structure of symptoms in patients with a first episode of psychosis.

BACKGROUND

The phenotype of psychotic disorders is presumed to be heterogeneous, but the best way to describe this heterogeneity remains unclear.

OBJECTIVE

To examine the lower-order and higher-order symptomatic architecture of psychotic disorders by means of factor analysis and the Schmid-Leiman transformation.

METHODS

Patients experiencing their first episode of psychosis (n=486) were comprehensively examined for 70 symptomatic variables, which were subjected to principal components analysis followed by a Promax rotation. First-order factors were subjected to second-order factor analysis, and influence of second-order factors on primary factors was removed using the Schmid-Leiman transformation.

RESULTS

First-order factor analysis revealed 13 primary factors that were substantially intercorrelated. Second-order factor analysis showed 5 higher-order factors with no substantial intercorrelations. The Schmid-Leiman transformation revealed that whereas the second-order factors accounted for most of the symptom covariance (63.5%), the first-order factors still accounted for an additional 36.5%. According to this transformation, five second-order factors (bipolar negative-mania, disorganization, psychomotor retardation, hallucinations and grandiosity) plus four first-order factors (depression, catatonia, bizarre delusions and paranoid delusions) best explained the factor structure of the symptoms.

CONCLUSIONS

The phenotype of psychosis is more complex than previously acknowledged as it embraces a multidimensional hierarchical structure organized into nonredundant first- and second-order factors.