Archive for September, 2009
September 24th, 2009
Why we keep making ‘slip errors’, even though we know what to do
As a good ergonomic citizen, I use an external monitor on my desk at work to reduce neck and back strain while I’m working. The set-up for this is simple:
- Plug in external monitor cable
- Open the Display Properties dialog
- Extend my desktop to the external monitor
Sounds straight forward, right? Well, despite successfully completing this process hundreds if not thousands of times in my life, I regularly forget to plug the damn monitor cable into my laptop before trying to complete steps 2 and 3. I’m talking at least once every two weeks, sometimes more. And no, I do not have below-average intelligence, but thanks for asking!
As it turns out, we all make similar mistakes even while completing procedures that we know inside-and-out. If you think I’m kidding, ask yourself if you’ve ever:
- Started typing in a web form only to realise that you forgot to position the cursor in the text entry box first
- Started typing in a different window on your computer, only to realise that you forgot to put focus on the window first
- Forgotten to attach an important document to an email before hitting the ‘send’ button
- Accidentally left the original in the photocopier after collecting the copies.
Aha! I bet I got you on at least one. These common mistakes are called ‘slip errors’, and they happen when you accidentally leave out a step in a task that you know well.
Slip errors are particularly common at the very beginning and the very end of tasks, especially when the error-prone step is more about setting-up for the main activity (as in the case of positioning the cursor before typing) or cleaning-up after the main activity (as in the case of retrieving the original from the photocopier).
So what’s the deal?
In my Master’s thesis I conducted research on these annoying little errors (which may be why I find it a little funny every time I make one). What researchers think is happening when we leave out a step like in the examples above, is that the device you’re using or operating has been designed so that a required step at the beginning or the end is functionally isolated from the main goal of the task. For example, when a web form is loaded in your browser, your main goal is to supply the information necessary to complete the form, not to click on the first form field. Or when you operate a photocopier, your main goal is to make the copies, not so much to deal with the originals. As such, your brain assigns less importance or salience to these functionally isolated steps, making you more likely to overlook them – especially if you’re tired, distracted, or especially focused on the outcome of the main task itself.
It also turns out that in some cases these errors are so pervasive that they are virtually impossible to eliminate without modifying the underlying device design, even with training. The best defence against them is to ensure that device design matches user goals – if tasks and devices can be designed so that all required steps that the user has to complete are related to achieving their goals, then slip errors can be greatly reduced or even eliminated.