Negative symptoms have long been recognized as a hallmark of schizophrenia. Newer evidence suggests that negative symptoms can be observed in persons with other disorders or even in non-clinical populations. However, most negative symptom scales are designed to identify clinically relevant symptoms, which might lead to underappreciation of subclinical symptom expression.

The aim of the present study was to establish distributional properties of well-established negative symptom scales in comparison with the newly developed Zurich Negative Symptom Scale, which employs a fully dimensional and continuous approach.

We included participants with established schizophrenia (n = 65), first-episode psychosis (n = 25), schizotypal personality traits (n = 29) and remitted bipolar disorder (n = 20). Assessment of negative symptoms was conducted with the Zurich Negative Symptom Scale and compared to establish rating scales.

In this broad sample, measurement of negative symptoms with established negative symptom scales lead to a highly skewed distribution. In other words, established negative symptom scales were able to identify negative symptoms in some participants in the non-schizophrenia spectrum, but a differentiation of negative symptom severity in the subclinical range was not possible. In contrast, the distribution of negative symptoms measured with the Zurich Negative Symptom scale approached normality.

Negative symptoms can be observed outside the schizophrenia diagnosis. However, in order to fully explore the continuity of negative symptoms, measurement instruments need to be designed to cover the full range of symptomatology starting at a subclinical level. We propose the newly developed Zurich Negative Symptom Scale as a useful tool in this respect.

The author has not supplied his declaration of competing interest.