Systems that performs some critical or very important actions tend to be harder to complete than non-critical actions.

For example, launching missiles might require the user to complete a complex activation sequence. On the other hand, some critical operations might need to be activated fast in case of emergency (fire alarms).

Where can I find some research or information about the trade off of easy to use vs. safety in the software area?

  • I can't verify if it answers your precise question, but there is MITRE's (the French defence systems contractor) report on designing interfaces in military applications. It's from the 70s, but the parts I've read remain very useful. [1]: hcibib.org/sam – Jimmy Breck-McKye Jan 19 '12 at 14:05
  • it looks interesting. unfortunately it doesn't say much besides what is already stated in the question – santiagozky Jan 20 '12 at 12:00

In this case, "safety" is commonly referred to as "reducing operator error" or "inadvertent user error"

Having an easy to use UI does not contradict having a mission-critical UI that minimizes operator error. For the classic nuke silo control panel, having two people turn keys to launch the missile is very easy in and of itself. However, your UI may require the user to expend more effort and time to reduce errors.

In most cases, reducing operator error requires additional steps in the interface, so the user has to expend more effort and/or re-confirm their intent. The easiest example of this is the classic "Are you sure you want to __?" dialogue box.

In mission-critical UIs, this trade-off of effort vs reducing operator error is typically based on two criteria:

  1. The severity of the error
  2. The likelihood the user will realize they made an error

In some cases, like accidentally launching a missile, the error itself is bad. Some famous plane crashes are due to pilots not realizing they have turned on the auto-pilot when it shouldn't be enabled. Turning the auto-pilot on isn't a sever error- it can easily be turned off. However, if the pilots don't realize they have the auto-pilot on, that could be bad.

A few resources on this are:

Nancy Leveson - Famous for her analysis of the Therac-25 accidents

2011 Catalogue of Human Factors, Safety and Risk books - Several of the books mentioned are on the topic you're interested in.

FAA Human Factors Design Standard - I find them a bit dry and tedious, but it may have concrete examples for you.

  • Hi Dave, great answer! Glad to have you :-) – Rahul Jan 21 '12 at 3:45

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