## 4 Discussion
The Mann-Whitney U tests showed that for the left-handed participants, the group with the relatively longer left thumbs statistically more often used their left thumbs to tap the key G, and the group with the relatively longer right thumbs statistically more often employed their relatively shorter left thumbs to tap the keys G and V and their right thumbs to tap the key Y. Simultaneously, for the right-handed participants, the group with the relatively longer left thumbs statistically more frequently used their left thumbs and relatively shorter right thumbs to touch the keys G and B, respectively, and the group with the relatively longer right thumbs statistically more frequently employed their shorter left thumbs and longer right thumbs to touch the keys T and B, respectively. In other words, it was difficult to find repetitive and clear patterns between the thumb choice (used to touch the keys) and the fact that the left or right thumb was relatively longer. Second, this finding might not be driven by the fact that which thumb, the left or right, was relatively longer. Regardless of whether the left or right thumb was relatively longer, the left thumb was statistically more often used for keystrokes on the key T in the left area, the keys G and V in the middle area of the QWERTY soft keyboard, and the right thumb statistically more often touched the keys B and Y in the right area of the keyboard. Interestingly, this was completely consistent with the aforementioned results that were induced by the tendencies to (1) employ the relatively closer one of both the thumbs for keystrokes and (2) use primarily the left thumb to tap the keys G and V due to the habitual experience from using a physical QWERTY keyboard. I.e., this means that this finding may not be due to the fact that which thumb, the left or right, was relatively longer or shorter but rather to the tendencies described above. In sum, from these contexts, it was not clear enough to conclude that this finding was purely the result of whether the left or right thumb was relatively longer. All things considered, the results of the present study can be summarized as follows. First, overall, the left thumb was used slightly more for keystrokes during two-thumb key entry on the QWERTY soft keyboard--in particular, the keys in the middle area were tapped preferentially by the left thumb, regardless of handedness. Second, most keys on the QWERTY soft keyboard were touched statistically more often by the relatively closer one of both the left and right thumbs, excluding the keys in the middle area. Third, noticeable differences were not found between the touch patterns of the left-handed and right-handed participants. Lastly, there was no clear evidence that the thumb choice for keystrokes on the QWERTY soft keyboard was significantly influenced by the fact that which thumb, the left or right, was relatively longer. Based upon these findings, in sum, for two-thumb key entry on a QWERTY soft keyboard, the distance between keys and thumbs was predicted to be the most important factor influencing the thumb choice for keystrokes, followed by the habits from using a physical QWERTY keyboard. This study can be extended in the following ways to address the knowledge gap and limitation and to achieve a better generalization of the results. First, a larger number of participants should be recruited for further study. The current study only included 36 participants due to the difficulty of recruiting left-handed participants. The number of participants may not be considered a small number, but they had to be divided into two groups (i.e., 18 left-handed and 18 right-handed) and examined separately in most analyses. Although this study showed statistically reliable results, we might have missed some noticeable thumb choice patterns for keystrokes or possible alternative conclusions, which could emerge if more participants were involved.