Editing Typing (section)

====Key strokes per character (KSPC)====
With the minimum string distance error, errors that are corrected do not appear in the transcribed text. The following example shows why this can be an important class of errors to consider:

''Presented Text'':       the quick brown<br />
''Input Stream'':         the quix<-ck brown<br />
''Transcribed Text'':     the quick brown

In the above example, the incorrect character ('x') was deleted with a backspace ('<-'). Since these errors do not appear in the transcribed text, the MSD error rate is 0%. That is the purpose of the key strokes per character (KSPC) statistic.

''KSPC'' = <math>(C+INF+IF+F)/(C+INF)</math>

There are some shortcomings of the KSPC statistic, such as:

* High KSPC values can be related to either many errors which were corrected, or few errors which were not corrected; however, there is no way to distinguish the two.
* KSPC depends on the text input method, and cannot be used to meaningfully compare two different input methods, such as a [[QWERTY]] keyboard and a multi-tap device.
* There is no obvious way to combine KSPC and MSD into an overall error rate, even though they have an inverse relationship.