Reducing number entry errors:
solving a widespread, serious problem
Example user interface
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Harold Thimbleby Swansea University |
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Paul Cairns York University |
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Safer number entry demonstration
Most number entry systems (such as calculators and drug infusion systems) ignore keying errors and may confuse users. The demonstration here shows how a clearer number entry system might work, preventing many keying errors that are usually ignored. The demonstration also provides clear error messages.
See “Please don’t sleep through this wake-up call” (2001) for an example of the dangers of misreading numbers, which this demonstration seeks to avoid. The story there sees the rules of clear number-writing as applying to written numbers only. In this demonstration, we show how the rules can be applied to safer number entry systems, not just for handwriting.
Compare the safer number entry system here with the problems of a typical conventional calculator here.
The International Campaign to Eliminate Use of Error-Prone Abbreviations
The interactive demonstration (use it on this web page) avoids the serious problems highlighted in an internationally-approved PDF list, which despite being a national campaign supported since 2006 by both the U.S. Food and Drug Administration and the Canadian Institute for Safe Medication Practices has been ignored by device manufacturers. The interactive demonstration on this page shows how the FDA/ISMP rules could be put into any interactive device to reduced undetected errors.
- The FDA/ISMP campaign is available here.
The interactive demonstrator...
Details
- Number entry systems usually display 0. or 0.0 before the user has keyed anything. If the user keys 0 or • or 0 • nothing will seem to happen, so in particular, if the display is 0., the user keying 5 might change the display to 0.5 or to 5. The demonstration here shows exactly what the user keys, and it is always predictable.
- Very few number entry systems group digits in threes to make them more readable. The demonstration does.
- Very few number entry systems have a clear decimal point. The demonstration has a large, highly-visible decimal point.
- Very few number entry systems make the decimal fraction smaller to be more obviously the fractional part of the number. The demonstration does.
- Few number entry systems check numbers while they are being keyed. Excess digits may be ignored. The demonstration here (arbitrarily) restricts numbers to have at most digits. (This limit can be changed.)
- The demonstration has both a clear key, Clear, and a last-key delete key, Delete.
- The demonstration imposes the Institute for Safe Medication Practices/Federal Drug Administration rules for clear numbers: there must not be a “naked decimal”; there must no terminal or leading zeros (except for numbers less than 1); and whole numbers must not have a decimal point.
- The demonstration has three key prompts (many number entry systems have none). They make the key insertion point clearer to the user, and they gently tell the user if the number is incomplete (e.g., has a naked decimal) or if there is an error.
- The decimal point key, &bull, is further away from 0 compared to most numeric keypads.
- On many devices, there may not be a dedicated Enter key, as here. For example, on a calculator, keys like + and = cause the number to be entered and processed.
Important details not demonstrated
- For many applications, something will be known about valid number ranges. For example, for drug doses it may be sensible to require standard units; thus 1 000 mg should be entered as 1 gm, and 0.1 gm should be entered as 100 mg. For many applications, only numbers in a valid range should be accepted (e.g., anything over 50 gm might be dangerous). Such issues are beyond the scope of this demonstration.
- For safety-critical number entry systems, an additional review step is normally required. Typically the device should ask the user to confirm they entered what they intended to enter. The review step is safer if the confirmation is not a literal confirmation, for example instead of saying “Confirm 48 hours” it might better say “Confirm 2 days” — the user knows what they keyed, and what they keyed may not be what they really intended, so it helps to convert it. The demonstration here does not ask for confirmation.
- When numbers are made of fixed-position digits (as is conventional, and is the option shown here) deletion is ambiguous: consider displaying 111 and hitting Delete, which will look very much like the left-most digit is deleted, not the right-most! (Left-alignment does not solve the problem.) The solution is to use horizontal animation, so on deletion, the digits are seen to move right. This solution is ideal for dot-matrix displays, but would be hard to simulate on conventional 7-segment displays.
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