Minimising Errors by Design

In Sect. 5.3.1 we discussed the concepts of slips and lapses and there are a number of design principles which can be employed to reduce the incidence of these. Slips for example can be addressed by avoiding common but not identical action sequences. Suppose viewing or cancelling an appointment requires an almost an identical series of mouse clicks. Should one of these activities be much more common than the other it is likely that from time to time an error will be made when actioning the infrequent task. Similarly buttons with unrecoverable consequences should be separated from more benign, frequently used functions. For example, it would be wise to design in some physical distance between buttons entitled Record patient death and Update patient address . 

A mode error is a particular kind of slip which has importance in technological systems. These occur when we believe a system to be in a particular state when in fact it is not. For example, a password may be repeatedly rejected because the user has accidentally pressed the caps lock key. The caps on mode renders the system into a state which was unexpected, unforeseen or forgotten. The use of modes in technology is often helpful as it reduces the command set and can produce a more compact user interface. However when relied upon in a safety critical business process, modes can present a significant hazard. 

A common example of a mode error in HIT systems is the use of filters to rationalise lists of data. Lists are commonly employed in user interfaces to create a master-detail workflow the list provides an overview of the available data which is linked to a second screen showing the complete dataset. Where lists have the potential to be long, designers sometimes provide a filter control. However clinicians use lists not just to ascertain what information is available but to establish what is missing. Suppose a system lists the immunisations which have been administered to a particular child. A clinician might scan the list to determine any which have been missed. Of course should a filter be inadvertently applied, wrong assumptions could easily be made. Designers who foresee this hazard will ensure that the presence and 

Users will quickly construct mental rules as they operate the systan for the first time. The assimilated rules empower than to go on to proficiently operate unfamiliar parts of the appUcation using the conventions learned in more accustomed areas. To achieve this designers need to strive for consistency in user interface design. For example, if some screens contain buttons labelled Save and Close whilst others have Okay and Cancel for the same functions, this is likely to prove confusing and hinder rule development In fact one of the least technically challenging enhancements to a user interface is to simply ensure that material is labelled appropriately, that abbreviations and ambiguities are avoided and button captions reflect their true function. 

Finally thought should be given as to how priority information should be handled in the user interface. The density of information can impact the ability to rationalise 

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