… you have used RECOMMENDED TARGET SIZES TAP GESTURES, but have found this range of target sizes does not provide an adequate solution for all tap target size-related issues due to screen real estate limitations.
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Using RECOMMENDED TARGET SIZES FOR TAP GESTURES is generally the most desired solution. However, the necessary screen real estate is not always available on smartphones.
Other interface elements might occupy most of the available screen real estate, depending on the particular function of each screen/page within the application structure, or you might need more tap targets than can comfortably fit on one screen when using RECOMMENDED TARGET SIZES FOR TAP GESTURES.
Opting for a range of smaller sizes than those that are considered to be ideal could solve the problem. In these cases, the trade-offs would be lower accuracy rates and higher task completion times for your users. Using a smaller target size is acceptable in such situations as long as you are aware that measures such as accuracy and task completion times will suffer. Inevitably, opting for smaller target sizes will cause the UI to be more difficult to operate and could result in some level of frustration and anxiety among users (Czaja & Sharit, 1998; Laguna & Babcock, 1997; Turner, Turner, & Van De Walle, 2007).
Therefore, it is important to understand within which range of smaller target sizes older adults’ mean accuracy rates and task completion times maintain themselves at an acceptable level, even though they will be naturally lower than when using RECOMMENDED TARGET SIZES FOR TAP GESTURES.
Our own research work suggests that older adults are able to use a certain range of smaller tap target sizes while still maintaining performance measures at satisfactory levels. This range of smaller target sizes includes those between 10.5 and 14 mm, where mean accuracy for the 14 mm targets was 93.75%, and mean task completion times were 1.94 seconds. Official guidelines recommend a minimum target size of 7 mm. However, for this target size participants’ mean accuracy decreased to 67.67%, and task completion times increased to 3.08 seconds.
When using RECOMMENDED TARGET SIZES FOR TAP GESTURES is not possible, and task completion times of 1.94 seconds are acceptable, use a minimum target size of 10.5 mm square.
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Czaja, S. J., & Sharit, J. (1998).Age Differences in Attitudes Toward Computers. The Journals of Gerontology Series B: Psychological Sciences and Social Sciences, 53B, P329-P340. doi: 10.1093/geronb/53B.5.P329
Laguna, K., & Babcock, R. L. (1997).Computer anxiety in young and older adults: Implications for human-computer interactions in older populations. Computers in Human Behavior, 13, 317-326. doi: 10.1016/S0747-5632(97)00012-5
Turner, P., Turner, S., & Van De Walle, G. (2007). How older people account for their experiences with interactive technology. Behaviour & Information Technology, 26, 287-296. doi: 10.1080/01449290601173499