Power Switches: Some User Expectations and Preferences

Three brief studies were conducted by the IBM Boca Raton Human Factors department to investigate user expectations and preferences regarding power switches. In the first study, 24 IBM employees were surveyed by showing them a power supply with a paddle switch in front. The results indicated that if the power switch was mounted vertically, 100% of the sample expected UP to be ON. When the switch was mounted horizontally on the front, 25% of the sample expected LEFT to be ON, and the other 75% expected RIGHT to be ON. Ninety IBM employees participated in the second study. The purpose of this study was to investigate the way people expect a rocker switch to work when it is located on the side of the machine. Overall, 46% of the sample expected the switch AWAY from the operator to be ON, and 54% expected the switch TOWARD the operator to be ON. In the third study, 49 IBM employees responded to a mailed questionnaire, and 24 participants from a temporary employment agency completed the same questionnaire. The results for the six items were: 1. For UP/DOWN switch: UP=ON: 97%, DOWN=ON: 03% 2. For LEFT/RIGHT switch: LEFT=ON:29%, RIGHT=ON:71% 3. For AWAY/TOWARD switch: AWAY=ON:52%, TOWARD=ON:48% 4. Style preference (IBM Employees), (Agency Personnel) UP/DOWN:94% UP/DOWN:58% LEFT/RIGHT:02% LEFT/RIGHT:29% AWAY/TOWARD:04% AWAY/TOWARD:13% 5. Location preference: FRONT:72%, SIDE:25%, BACK:03% 6. Side preference: LEFT:10%, RIGHT:90% Since it appears that virtually 100% of users have the same expectation regarding the operation of a vertical power switch, designers should avoid using other power switch orientations. This is not a critical design issue, but it is better to design machines the way that users expect them to work.