Choosing negative symptom instruments: issues of representation and redundancy

Assuming that the negative syndrome in schizophrenia may be multidimensiona l, this study examines how conclusions about the structure of negative symp toms may be influenced by the particular rating scale used, the level of da ta reduction used (such as total, subscale and individual item scores), and also the type of data analyses used to compare scales. Forty-seven subject s with RDC schizophrenia were rated on three instruments: the negative symp tom subscale of the BPRS (BPRS-WR); the negative symptom subscale of the PA NSS (PANSS-NS); and the SANS. Comparisons were made of different levels of data reduction and different methods of analysis, which included bivariate correlation, bi-multivariate canonical correlation and redundancy analysis. We found that while the total scores from all three scales were highly cor related and therefore highly redundant, both the individual items and subsc ale scores from the SANS contained information independent of the BPRS-WR, and also, to a lesser extent, of the PANSS-NS. When the BPRS-WR was correla ted with either the SANS or the PANSS-NS, one strong canonical variate (CV) emerged, on which all or most items loaded, particularly the affective ite ms. When the SANS and PANSS-NS were correlated, this component again emerge d along with three less strong but interpretable components. When examining the non-symmetrical redundancy, we found that the BPRS-WR variates explain ed 40% of the SANS variance, while conversely the SANS variates explained 8 0% of the BPRS-WR variance. The PANSS-NS variates were found to explain 58% of the SANS variance, while the SANS variates explained 85% of the PANSS-N S variance. Finally, the PANSS-NS variates explained 79% of the BPRS-WR var iance, while conversely the BPRS-WR variates explained 54% of the PANSS-NS variance. All three scales appear to measure a single general 'affective' c omponent of the negative syndrome, while the PANSS-NS and the SANS also cov er additional components which identify cognitive, anergic and social dimen sions. This extra information is lost, however, if inappropriate data reduc tion and/or statistical analyses are used. The fact that the three instrume nts predicted the various dimensions of the negative syndrome to different degrees suggests that the best choice of a negative scale depends on the ty pe of information required. Nevertheless, further examination of how negati ve symptom scales cover the multi-dimensional nature of the negative syndro me is required. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.