  During lab studies of text entry methods it is typical to observer very few
errors in participants' typing - users tend to type very carefully in labs.
This is a problem when investigating methods to support error awareness or
correction as support mechanisms are not tested. We designed a novel evaluation
method based around injection of errors into the users' typing stream and
report two user studies on the effectiveness of this technique. Injection
allowed us to observe a larger number of instances and more diverse types of
error correction behaviour than would normally be possible in a single study,
without having a significant impact on key input behaviour characteristics.
Qualitative feedback from both studies suggests that our injection algorithm
was successful in creating errors that appeared realistic to participants. The
use of error injection shows promise for the investigation of error correction
behaviour in text entry studies.
