Input context efficiency is a qualitative metric on how long before a user’s hand switches to a different device. It is a term I coined up, I am not sure if it is used anywhere else (and it is not in Google at the time of writing this article). I alluded to this on my KDE vs everything else rant.
Why is this important?
Efficiency, accessibility, and recovery.
As a user gets familiar with a user interface, more efficient users would look for shortcuts to reduce the amount of mouse clicks or typing they would need to do. The more that can be done with one device, the better the metric.
By allowing more to be done from many devices, we make the application more accessible to more people. Some people may be able to use the keyboard, but not the mouse. Some people might only have one hand. And some might not have any hands. However, this metric is limited to input accessibility not output such as screen or text to speech.
Sometimes our input devices fail or can’t get recognized. For example, you wireless mouse runs out of batteries, but you still need to work with the system. If you can do everything that you need on the keyboard (although slower since there is stuff to learn) then at least you can get your job done.
What should be done by the mouse and what should be done by the keyboard?
The mouse is a pointing device, so the action that is best done by a mouse is to actually point at some arbitrary location on the screen.
The keyboard is a typing device, so the action that is best done by a keyboard is to type in text.
How would I quantify this metric?
You can quantify how many actions can be performed on one device but not the other, or requires both devices. That would give you a number to go with. Of course two things that should be ignored are “pointing” on the keyboard and “typing” on the mouse since that does not make any sense. Although you can put that in your metric, but your target would be 1 (unless you really work hard).
In order to save time, its best to just measure two metrics what can be done on the mouse alone that cannot be done on the keyboard and what can be done with a mouse and keyboard that cannot be done by the mouse alone. Those two metrics show how efficient you can be with just the keyboard and the mouse alone, which is the most useful metrics you would get with regards to efficiency.
Another metric that should be measured is how easy is it to figure out all the shortcuts? This metric is pretty simple to calculate anyway as most systems only require one step to do a major portion of the shortcuts and that is to display the menu bar which should list down the hotkeys.
What about other input devices?
You can measure the same metrics with other input devices such as voice input, eye tracking devices, touch screens. Having support for more devices increases accessibility of your application to more people who may be disabled.
What system provides the best metric?
Microsoft Windows and most (if not all) Microsoft applications would have the best metric if it were ever calculated. I think Internet Explorer 1.0 is the only Microsoft application that I really needed a mouse for.
In Windows, window management functions are accessible through the keyboard using Alt-Space to bring up the window menu.
Drag and drop operations which are normally the domain of the mouse can be done through copy and paste keys from the keyboard.
If the keyboard does not work, we have “charmap” or a software keyboard to help us type in case of such emergencies.
Some keyboard and mouse combinations such as holding down control, then drag and drop a file to copy can be done with just the mouse alone. This is done by dragging and dropping with the right mouse button, upon a drop it brings up a popup menu to specify the drop action. To find out a major portion of the hotkeys available, Windows applications require just one key Alt or F10 which brings up the menu bar of the application. To bring up the Start menu, it is just the Window key. Unfortunately, there is no way to figure out the Window key shortcuts unless you search the help, read books or Google, but those are more advanced shortcuts so its no big deal.
What system provides the worst metric?
The failsafe X window system provides the worst metric. Without the mouse you won’t be able to select the xterm and you’re stuck. Unless the X server provides a way of emulating the mouse through the keyboard. Mind you this is not the norm, we have a lot of Window Managers that allow the user to hotkey everything related to window management. GTK is probably the worst one I have used when it comes to the popular toolkits for Linux (so not including Xt or CDE or Motif). I find that I need to switch between keyboard and the mouse quite often because some widgets such as the combo box cannot be focused using just the keyboard alone on some GTK applications. In GTK or KDE you have F10 to bring up the menu which is great. Unfortunately, it does not span to the window management. So if you press left on the first menu entry, it does not go to the Window managment menu.
What about the Mac?
I haven’t use the Mac much so I haven’t figured out all the keyboard shortcuts yet. However, with the notion of a one button mouse, a lot things operations that deviate from the norm such as copying files rather than moving require pressing something on the keyboard. So users would have one hand on the mouse and one hand on the keyboard. So if you get into an accident and one arm is in a cast, tough luck if you need to perform operations that would require two hands available. I also haven’t found a way of going to the menu bar without the mouse using a single keyboard press, I am pretty sure there should be one, just haven’t found it yet. Fortunately Macs now support the right mouse button if you have an external mouse (too bad MacBooks only have one button for the trackpad).
Conclusion
There are a lot of literature and metrics out there regarding how to make user interfaces as easy to use as possible for newbies. However, this metric is not targeted for newbies but normal and power users of the system. From my experience:
- Microsoft is the leader when it comes to this metric,
- Apple may be a close second (need more time to use it),
- QT on X does most of it quite well, except it does not go into the Window manager (mind you I am using Emerald). This is number 3 out of 4.
- GTK on X based applications are the worst.
