Table 1.

Representative examples of usability principles, violations and remedies

Usability principle22	Description	Usability violation	User centred design remedy
Visibility of System Status	The system should always keep the user informed about what is going on through appropriate feedback within reasonable time.	Two different order entry modes (search and catalog) are virtually identical and easily confused. User may be unable to complete a specific order if the wrong mode is in use.	There is only one order entry mode. This mode allows user to accomplish all order entry tasks.
Consistency	The user should not have to wonder whether different words, situations, or actions mean the same thing.	Drug information is inconsistently displayed during an ordering task. For example, the user selects morphine 1 mg po q4h from the drug catalog, which appears as ‘morphine sulfate q4h po 1 mg’ on another screen.	Drug information is consistently displayed throughout the ordering task.
User Control and Freedom	After choosing a system function by mistake, the user needs a clearly marked ‘emergency exit’ to leave the unwanted state without having to go through an extended dialog.	There is no obvious way to undo actions. The user must learn to right click on the order then select ‘undo’ from the bottom of a long drop down list.	User selects an order with a left mouse click, and deselects the same order with another left mouse click. There is no need to right click and no need to select the ‘undo’ action from a drop down list.
Help Users Recognize, Diagnose and Recover from Errors	Error messages should be expressed in plain language (no codes), precisely indicate the problem and constructively suggest a solution.	User cannot easily see a list of all orders prior to submission, so errors are difficult to recognize.	All orders are fully displayed on a single screen for review throughout the ordering process.