Factor structure of the Neurological Evaluation Scale in a predominantly African American sample of patients with schizophrenia, unaffected relatives, and non-psychiatric controls

Abstract

Objective This study aimed to identify latent factors of the most widely used scale to measure neurological soft signs, the Neurological Evaluation Scale (NES), in a sample of schizophrenia patients, their relatives, and non-psychiatric controls. Method The NES was administered following the format and instructions of the original scale [Buchanan, R.W., Heinrichs, D.W., 1989. The Neurological Evaluation Scale (NES): a structured instrument for the assessment of neurological signs in schizophrenia. Psychiatry Res. 27, 335–350]. Three factor analyses were conducted using: (1) 23 items of the scale, (2) these 23 items in a sample restricted to African American participants, and (3) 12 items previously recommended based on adequate inter-rater reliability [Sanders, R.D., Forman, S.D., Pierri, J.N., Baker, R.W., Kelley, M.E., van Kammen, D.P., Keshavan, M.S., 1998. Inter-rater reliability of the neurological examination in schizophrenia. Schizophr. Res. 29, 287–292]. Results Exploratory factor analysis in the overall sample ( n = 110) revealed three factors of interest: a “coordination/Romberg” factor (which included the fist-edge-palm test, finger-thumb opposition, rapid alternating movements, and the Romberg test), a “sensory integration” factor (which included synkinesis, extinction, stereognosis, and audio-visual integration), and an “eye movements/tandem walk/overflow movements” factor (which included convergence, gaze impersistence, tandem walk, and adventitious overflow). Minimal differences were apparent when comparing these results with those obtained from an analysis including only African American participants ( n = 99). Restricting the analysis to only 12 items resulted in two factors (with poor discriminant validity and internal consistency), which showed few similarities with previously reported exploratory factor analysis results. Conclusions This study shows that results of empirically-derived factors of the NES vary substantially across study samples and research groups, though there appear to be at least two consistent latent variables, one related to the repetition of motor tasks and another tapping the processing of sensory stimuli. The factors demonstrated in the present study are more consistent with the original conceptually-derived subscales than prior factor analyses. Thus, until further research replicates consistent subscales of subtle neurological impairment in a variety of settings and samples, the total NES score may be more useful when comparing results across studies. Further research on latent neurological factors is needed.