Abstract. The present article is concerned with the theoretical foundations and practical aspects of developing pictorial scales. It aims to assess the potential of pictorial scales compared to verbal scales. The article provides a review of existing pictorial scales with a view to identifying suitable methodological approaches for developing such scales. The review showed that the development and especially validation of many pictorial scales did not follow a stringent methodological approach. A category system is proposed, which allows the classification of different types of pictorial scales. Finally, we present a first draft of a theoretical framework, which can provide guidance for the future development of pictorial scales. The present work carries the implication that a specific methodological approach is needed, which focuses more strongly on the particular needs of designing pictorial scales (e.g., testing the comprehensibility of pictures).

We have developed a pictorial multi-item scale, called P-SUS (Pictorial System Usability Scale), which aims to measure the perceived usability of mobile devices. The scale is based on the established verbal usability questionnaire SUS (System Usability Scale). A usercentred design process was employed to develop and refine its 10 pictorial items. The scale was tested in a first validation study (N=60) using student participants. Psychometric properties (convergent validity, criterionrelated validity, sensitivity, and reliability), as well as the motivation to fill in the scale were assessed. The results indicated satisfactory convergent validity for about twothirds of the items. Furthermore, strong correlations were obtained for the sum scores between verbal and pictorial SUS, and the pictorial scale was perceived as more motivating than the verbal questionnaire. The P-SUS represents a first attempt to provide a pictorial usability scale for the evaluation of (mobile) devices.

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