Objectives. To design a brief measure to assess both the severity of paranoid thinking and the perceived deservedness of persecution, which can be employed in clinical and non-clinical populations.

Background. No existing measure is adequate for these purposes.

Methods. In Study 1, we selected 10 items for a persecution and deservedness scale (PaDS) using data from 318 UK and 290 Portuguese undergraduate students, who also completed the Beck Depression Inventory and the Fenigstein's Paranoia Scale. In Study 2, we made comparisons between 45 clinical participants with a diagnosis of schizophrenia, schizoaffective disorder or delusional disorder and the UK students from Study 1. The psychometric properties of the PaDS were analysed for separate persecution (P) and deservedness (D) subscales.

Results. The 10-item PaDS subscales were internally reliable for both clinical and student samples. Correlations with other measures of depressive mood and paranoid thinking indicate that the P subscale has concurrent validity. Higher P and D scores were observed in UK students compared to Portuguese students. The clinical participants' P scores subscale were significantly higher than the students' scores but their D scores were lower.

Conclusions. The PaDS is a reliable and valid measure of paranoid thinking and perceived deservedness of persecution, which is sensitive for use in clinical and non-clinical populations. Paranoid thinking appears to be mainly bad-me in non-clinical groups but poor-me in psychotic psychiatric patients.