Table 3.

Usability problems in version 2 of all 3 self-tests, rate of errors, and solutions (n=134).

Problem ID	Usability problem	Rate of errors/trials	Improvements made
1	Incorrect performance	66/402 (16%)	Added new, improved instructions to the videos (new voiceover and added graphical elements to draw attention to the details of the test procedures); added a warning message that appears if trying to start the test without watching instructions; and added real-time TTSa voice feedback on the number of repetitions in the Self-STSb
2	Started performing test (during instruction video) without starting the test in the app	28/402 (7%)	Changed structure of the app: main window now has two separate buttons, one for “start test” and one for “instructions”
3	Did not sit still and wait for start signal after test was started in the app	39/268 (15%)	Added real-time verbal step-by-step instructions that are initiated after the test is started in the app
4	Incorrect placement of phone	11/402 (3%)	Added real-time verbal instruction explaining where to place the phone and when to do this
5	Did not hear/perceive instructions	4/402 (1%)	Changed settings in the app so that the volume is always on maximum levels during testing, to prevent participants from accidentally pressing the “volume down” button
6	Accidentally cancelled the test	8/402 (2%)	Reduced the size of the “stop” button

^aTTS: text-to-speech.

^bSTS: Sit to Stand.