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A Study of the Effect of Thumb Sizes on Mobile Phone Texting Satisfaction

Vimala Balakrishnan and Paul, H.P. Yeow

Journal of Usability Studies, Volume 3, Issue 3, May 2008, pp. 118-128

Article Contents

Thumb measurements

Researchers recorded the subjects thumb length and circumference. Thumb length might affect users' reachability of the keys whereas users with large thumbs might find it cumbersome keying in messages via the tiny keys. Thumb length was measured from the second joint of the thumb to the tip of the thumb. The thumb circumference was measured above the second joint of the thumb at the narrowest point (see Figure 3). The measurements were taken twice using a measurement tape, then the two measurements were averaged together to maintain consistency.

Figure 3. Thumb measurements

Table 2 shows the summary statistics for these anatomical measurements based on genders. These measurements depict the readings for the dominant thumbs that are used to text.

Table 2. Thumb length and circumference statistics
Male (N=55)
Mean SD (min.-max.)
Female (N=55)
Mean SD (min.-max.)
Thumb length 6.4 0.8 (4.8 - 8.0) 5.4 0.65 (4.2 - 7.5)
Thumb circumference 5.8 0.75 (4.5 - 7.8) 5.4 0.58 (4.5 - 7.2)

Interview questionnaires

An interview questionnaire was designed based on Sinclair's (1995) guidelines, and then tested on five subjects and revised before finalizing it. The questionnaire was developed in English and had two major sections. Section A was to obtain the demographic profile of the subjects and the mobile phone characteristics. This section consisted of questions addressing issues such as dominant hands, finger(s) used when composing messages, and experience in using SMS. Section B is for the subjects to rate their satisfaction or dissatisfaction levels of SMS usage based on the keypad design factors using Likert's five-point scale (1 means "Strongly dissatisfied," 2 means "Dissatisfied," 3 means "Neutral," 4 means "Satisfied," and 5 means "Strongly Satisfied").


Face-to-face interviews were conducted using the questionnaire beginning with the subjects' background information, which included their age, gender, years of experience in sending SMS, the finger(s) used in composing SMS, and so forth. The interviewer recorded the subject's thumb measurements. Then the interviewer recorded mobile phone characteristics such as brands, dimensions, and support of predictive text entry. Subjects were encouraged to give comments, opinions, and suggestions. All verbal comments were recorded by the interviewers. Each interview session lasted for about 30 minutes. It took two interviewers approximately six to seven weeks to question the subjects. The interviewers were knowledgeable of mobile phone features and SMS application so that they could easily interact with the subjects during the interview sessions.

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