Table 2.

Usability problems in version 1 of the Self-Timed Up and Go and Self-Tandem apps, rate of errors, and solutions (n=189).

Problem ID	Usability problem	Rate of errors/trials	Improvements made
1	Incorrect performance	120/378 (32%)	Added instruction video
2	Performed test without starting app	22/378 (6%)	Implemented instruction video that clearly demonstrates that the play button needs to be pressed before performing the test
3	Did not sit still and wait for start signal after test was started	23/189 (12%)	Added instruction video (demonstrating sitting still and waiting for the start signal before starting the test) and shortened the delay in the algorithm to limit any confusion
4	Incorrect placement of phone	32/378 (8%)	Changed placement to front pocket for Self-TUGa and Self-STSb and added a reminder in the countdown screen on what to do first (eg, “put the phone gently in your pocket”)
5	Did not hear/perceive instructions	18/378 (5%)	Changed placement to front pocket for Self-TUG and Self-STS
6	Accidentally cancelled the test	15/378 (4%)	Not possible to override the home button function in the android OS, change of placement the preferred solution to reduce this problem

^aTUG: Timed Up and Go.

^bSTS: Sit to Stand.