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I've noticed in some tasks that require very fine precision with the mouse, that the act of physically clicking the button is sometimes enough to move the mouse. In an extreme case, I watched an elderly newbie who was unable to double-click without dragging or moving the mouse between clicks.

I've also noticed a direct analogy with touch screens - having moved the pointer to exactly where I want it, I cannot lift my finger from the screen without dislodging the pointer.

I would like to learn more about this phenomena, how common it is, and techniques used to overcome it, but before I can do that, I need to know if it has a name...

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    If you observe such problems, it means the system isn't properly designed (small target areas) or configured (movement tolerance for physically disabled people).
    – dnbrv
    Commented Feb 9, 2012 at 5:15
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    @dnbrv: Agreed. But how can I point to best practices until I know what to search for?
    – Oddthinking
    Commented Feb 9, 2012 at 7:33
  • You should search for best practices in touch target areas and in designing for physically disabled users.
    – dnbrv
    Commented Feb 9, 2012 at 12:40

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A general term for these is Performance error as the linked journal article mentions. These can be caused by motor difficulties, literal fat fingers, accidental movement or an incorrect assumption of where the virtual cursor will land.

A touch screen specific problem is the offset from where the user presses, and offset could also describe the excessive movement from a first click point that causes a double click to fail.

With induction pens and resistive screens the touch point might be slightly off from where the computer reads the input as a result of calibration; I never have problems with mouse double clicking but on my first Tablet PCs I had to specify a specific double click distance as I noticed it's much easier to click outside the allowed area.

Capcative touch screens generally don't have this problem but due to using your fingers two problems arise; you can't see the touch point anymore, and your exact touch point is offset from where you think you're pressing. You may think you're about to press a button with the tip of your finger, but accidentally touch the next button down with the pad of your finger if they are'nt properly spaced and you aim low on the first button.

There's a fair body of research in HCI in regards to touch screen offsets for pen/touch interactions. A common suggestion is an offset cursor which shows above the pen/finger tip, offset enough that the user can see it even when their input method covers the touch point.

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"Fat fingers" is a common term associated with touch screen interfaces. Jakob Nielsen uses it in his article Kindle Fire Usability Findings.

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I am not aware of a term that describes this, but it is definately a design flaw if the user cannot accurately interact with it the way they were intended to. Might need to come up with a new term like "interactive tolerance analysis or optimization"

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    Be careful with that, it sounds complicated enough to catch on :). In a couple years we'll all be Interactive Tolerance Analysts and Optimizers.
    – Vitaly Mijiritsky
    Commented Feb 9, 2012 at 6:10
  • LOL!!! well at least we'll be the first right?...
    – Ely Solano
    Commented Feb 9, 2012 at 8:40
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Sausage fingers, though with touch screens it happens a lot to average users too.
And this is the reference for the origin of the name.

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  • He, I checked the reference, but it doesn't mention the term.
    – Oddthinking
    Commented Feb 9, 2012 at 13:13
  • I know, but that was the inspiration for the term. I am not sure who originally coined the phrase though.
    – Danny Varod
    Commented Feb 9, 2012 at 14:21
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I'm not aware of a specific term, but I'd advise looking at Fitt's law http://en.wikipedia.org/wiki/Fitts%27s_law in the first instance, as will almost certainly have been referenced by any work in this area.

For example:

Fitts' Law for Older Adults: Considering a Factor of Age http://dl.acm.org/citation.cfm?id=1497502&dl=ACM&coll=DL&CFID=83979140&CFTOKEN=47971311 ("On average, it took elder participants twice as much time to complete movement tasks, but their accuracy was two times higher. Error level was affected by small (8 pixels) target size, but not by movement distance.")

Comparison of mouse performance between young and elderly ... http://ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F8325%2F26342%2F01167981.pdf%3Farnumber%3D1167981&authDecision=-203

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    Fitts's law has nothing to do with double clicks or accuracy of positioning. It's about the time needed to locate a control when moving within an interface.
    – dnbrv
    Commented Feb 9, 2012 at 14:20
  • Fitt's law doesn't reference clicks; although it is concerned with the accuracy of positioning (not sure why you'd say it isn't?) - from the Wikipedia page: "From the equation, we see a speed–accuracy trade off associated with pointing, whereby targets that are smaller and/or further away require more time to acquire.". I mention it because it's the most relevant piece of formal work, and hence likely to be a good starting point for any work in this area.
    – Peter
    Commented Feb 9, 2012 at 14:44
  • The law itself is a formula to find the time needed to reach a control within an interface based on the distance between current position & the control and the size of the control along the axis of movement. Accuracy deals not only with time but also with not triggering other controls.
    – dnbrv
    Commented Feb 9, 2012 at 14:53
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I suggest what you actually want to look at is what MS Windows calls its 'Accessibility Controls'. Its one of the control panels.

So the search term you want is 'Accessibility'

Here's a rather out of date article on various settings to play with for older users:

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