The validity of the Seasonal Pattern Assessment Questionnaire (SPAQ) in diagnosing Seasonal Affective Disorder is questionable. In 2004 the Seasonal Health Questionnaire (SHQ) was proposed as a more appropriate screening instrument for depression with a seasonal pattern.

To compare the performance of the SPAQ, the most commonly used tool for assigning a diagnosis of SAD, with the SHQ, which uses the DSM-IV criteria for recurrent depression with seasonal pattern.

Two samples of approximately 200 medical students in Tromsø, Norway (69° north) and Ferrara, Italy (44° north), filled in both questionnaires. Prevalence of recurrent depression with seasonal pattern was calculated according to gender and latitude of living, with both instruments. Using SHQ diagnosis as the gold standard, sensitivity and specificity of the SPAQ as a diagnostic instrument was ascertained.

The prevalence of depression with seasonal pattern measured by SPAQ was 12% in Norway and 14.5% in Italy, the difference was not significant. Prevalence was highest in females in both countries (Norway: males 4.2%, females 14.7%, Italy: males 2.3%, females 18.8%), but the difference was only significant in Italy (p = 0.007). According to SHQ, the corresponding figures in Norway 5.9% and 7.1% (p = 0.77) and in Italy 3.9% and 3% (p = 0.75). The specificity of the SPAQ was 88.8% and the sensitivity was 47.3%.

Compared to a DSM-IV diagnosis of depression with seasonal pattern as measured by the SHQ, the SPAQ seriously overestimates the prevalence of seasonal depression, especially in women, and the sensitivity is far too low.