A demonstration is presented of how automated reasoning tools can be used to check the predictability of a user interface. Predictability concerns the ability of a user to determine the outcomes of their actions reliably. It is especially important in situations such as a hospital ward where medical devices are assumed to be reliable devices by their expert users (clinicians) who are frequently interrupted and need to quickly and accurately continue a task. There are several forms of predictability. A definition is considered where information is only inferred from the current perceptible output of the system. In this definition, the user is not required to

Differential formal analysis is a new user interface analytic evaluation method based on stochastic user simulation. The method is particularly valuable for evaluating safety critical user interfaces, which often have subtle programming issues. The approach starts with the identification of operational design features that define the design space to be explored. Two or more analysts are required to analyse all combinations of design features by simulating keystroke sequences containing keying slip errors. Each simulation produces numerical values that rank the design combinations on the basis of their sensitivity to keying slip errors. A systematic discussion of the simulation results is performed for assessing the causes of any discrepancy, either in numerical values or rankings. The process is iterated until outcomes are agreed upon. In short, the approach combines rigorous simulation of user slip errors with diversity in modelling and analysis methods. Although the method can be applied to other types of user interface, it is demonstrated through a case study of 5-key number entry systems, which are a common safety critical user interface style found in many medical infusion pumps and elsewhere. The results uncover critical design issues, and are an important contribution of this paper since the results provide device manufacturers guidelines to update their device firmware to make their devices safer.

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Empirical methods and analytic methods have been used independently to analyse and improve number entry system designs. This paper identifies key differences in exploring number entry errors combining laboratory studies and analytic methods and discusses the implications of triangulating methods to more thoroughly analyse safety critical design.Additionally, a previously presented analytic method used to analyse number entry interfaces is generalised to analyse more types of number entry systems. This paper takes "number entry" to mean interactively entering a numeric value, as opposed to entering a numeric identifier such as a phone number or ISBN. Many applications of number entry are safety critical, and this paper is particularly motivated by user interfaces in healthcare, for instance for specifying drug dosage.

Abstract-The design of medical devices directly affects the way healthcare practitioners carry out their daily tasks. Users welcome design that takes into account the clinical environment, in which the device is operated and is compatible with their workflow. However, if the design fails to fit, the likelihood of errors increases, which will put patient safety at risk. In this paper, we report current practice related to UCD (User Centred Design) in the context of medical device, focusing on end user feedback mechanisms deployed in pre-market and post-market phases of the device lifecycle. The results of an interview and workshop study are reported, revealing shortcomings in current feedback channels. In reaction to these shortcomings, we discuss the advantages and feasibility of enabling automatic feedback channel in medical device design, to ensure the quality and the effectiveness of feedback.