For the 16 negative stigma items, the original validation reported: Total Negative Stigma: α = .81; Stigma Agreement: α = .75; Stigma Awareness: α = .71. For the 8 positive items: Total Positive: α = .67; Intellectual Ability: α = .67; Recovery: α = .74; Friendship: α = .44. Thus, reliability was acceptable for the principal negative stigma scales, but weaker for the positive scale—particularly the two-item Friendship component. A subsequent Spanish validation reported substantially stronger internal consistency for its negative (α = .94) and positive (α = .81) scales.

Test–retest reliability was evaluated in 109 young people over two weeks. Correlations were: Stigma Agreement: r = .68; Stigma Awareness: r = .75; Total Negative Stigma: r = .75; Total Positive: r = .65. These findings provide evidence of moderate-to-good short-term stability, particularly for the overall negative stigma score and Stigma Awareness.

The original study conducted separate principal components analyses for the negative and positive items because young people showed different response patterns to positively and negatively worded statements. Negative stigma items A two-component solution was identified: Stigma Agreement – personal endorsement of stigmatising statements Stigma Awareness – awareness of prevailing societal stigma. The two components explained 35.66% of variance. Factor loadings ranged from: Stigma Agreement: .492–.679 Stigma Awareness: .420–.643. Positive items Three components were identified: Intellectual Ability; Recovery; Friendship. Together these explained 61.02% of variance. However, the original analysis was exploratory and used PCA rather than CFA. A later study by Nearchou et al. (2021) re-examined the factorial structure in 963 participants aged 12–25 years. It retained 11 of the original 16 negative items and confirmed a two-factor solution representing Stigma Agreement and Stigma Awareness. The authors recommended this shorter revised version for future research

The original study provides preliminary evidence of construct/discriminant validity. As predicted, greater personal stigma was associated with lower prosocial behaviour. Positive and negative attitudes were also inversely associated. The study also demonstrated an important theoretically expected distinction between personal and societal stigma. Young people reported significantly greater Stigma Awareness than Stigma Agreement. Indicating young people perceived stigmatising attitudes as more prevalent in society than they personally endorsed them.

Formal measurement-invariance analysis was not conducted in the original 2015 validation. The original study found no significant differences according to parental education/socioeconomic proxy. However, primary- and secondary-school pupils differed on negative stigma scores, with older participants generally reporting greater stigma; they did not differ significantly on the positive-attitudes score. Subsequent Spanish validation (de la Higuera-Romero, J., et al., 2022). formally examined measurement invariance across sex and found the PMHSS-24 to be invariant between male and female adolescents.