Keywords

1 Introduction

According to the Ministry of Health and Welfare of Korea in 2020, the rate of physical disability among community-dwelling people with disabilities were the highest [1]. People with severe physical disabilities use mobility assistive devices when moving to the community. Among them, powered wheelchairs are generally used when users cannot propel independent wheelchairs, and according to Lee’s study, powered wheelchair users reported low satisfaction with the weight and size of powered wheelchairs and post-service [2]. Accordingly, Lightweight Power Wheelchairs (LPW) with the function of powered wheelchairs at home and abroad are being studied [3,4,5,6].

Usability is specified according to the ISO-9241-11 guidelines, and usability testing is to investigate the interaction between users and products in the process of constructing and executing usability scenarios [7]. According to Kim, in order to increase the usability of assistive devices, it is important to reflect the needs of the people of disabilities from the early stage of development, and to this end, usability testing is required [8]. However, research on usability testing of LPW is insufficient at domestic and abroad.

Kim conducted a comparative usability testing on a hybrid manual-powered wheelchair but focused on wheelchair driving [9]. In the case of people with severe physical disabilities, it is difficult to manage independent powered wheelchairs, so help from caregivers is essential. Accordingly, it is important to find out the usability of wheelchairs from the perspective of caregivers in product development and improvement [10].

Therefore, in this study, we would like to compare the usability of two LPWs recently developed in Korea in accordance with the ISO-9241-11 guidelines from the perspective of users and caregivers. Through the analysis of the usability testing results, we intend to derive factors to be considered in order to increase the usability of users and caregivers and to provide basic data for future LPW research.

2 Method

2.1 Participants

Participants in this study were recruited from people with physical disabilities who use powered wheelchairs. According to Nelson’s research, 5 people with physical disabilities who agreed to participate in the study were finally selected [11]. The general characteristics of the study participants are shown in Table 1.

Table 1. Characteristics of participants
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2.2 Inclusion and Exclusion Criteria

If the participants met (1) A power wheelchair can be used independently and (2) There is no cognitive difficulty in understanding the research process and agrees to the research voluntarily, they were included in the study, and if they met (3) Do not currently use a powered wheelchair and (4) Participant currently has difficulty using an power wheelchair, they were excluded from the study.

2.3 Tools

2.3.1 Lightweight Power Wheelchair

In this study, two types of LPW manufactured in Korea were used (Fig. 1). Unlike existing power wheelchairs, it is light in weight and can be folded and stored, so it can be carried in a vehicle. Another advantage is that the battery can be easily installed and removed. It is equipped with the same driving device as the existing power wheelchair and can be steered and speed controlled using a controller such as a joystick.

Both LPWs have the same 8-inch front wheel and 14-in. rear wheel. The battery capacity of the two LPWs is the same at 24 V and 16 Ah. The motor specifications of the two LPWs are the same at 250 W and 4600 rpm. The controller of both LPWs is the same. The weight of the two LPWs is different. The weight of LPW1 is 29.7 kg, and the weight of LPW2 is 31 kg. The frame sizes of the two LPWs are different. LPW1 is 105–58–84 cm (length, width, height), LPW2 is 103–58–96 cm (length, width, height).

Fig. 1.
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Lightweight power wheelchair

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2.4 Usability Testing

In the International Organization for Standardization (ISO), usability is defined according to the ISO-9241-11 standard. Usability refers to effectiveness, efficiency, and satisfaction when a user uses a system, device, or service to achieve a specific purpose [12]. Effectiveness is to measure whether the user has performed the desired task accurately and perfectly. Efficiency includes time, costs invested to achieve goals, the degree of effort, and fatigue. Satisfaction is the evaluation of an individual’s cognitive, emotional, and psychological responses, such as comfort and positive attitude, when a user performs a task using a product [12, 13]. Effectiveness was measured through task success. Efficiency measured (1) task performance time (TPT), (2) effort and fatigue required to perform tasks using the product through The Borg Rating of Perceived Examination Scale (RPE), and (3) subjective difficulty when performing tasks through the Differential Rating Scale (DRS). Satisfaction measured acceptance, satisfaction, and overall usability of the product through (1) Acceptability Rating Scale (ARS) and (2) System Usability Scale (SUS) [14,15,16,17]. RPE is measured in the range of 6 to 20 points, 6 points are no exertion, 20 points are interpreted as maximum exertion, DRS is interpreted as −3 points to 3 points, −3 points to very difficult and 3 points to very easy. ARS ranges from −3 to 3 points, and −3 points are interpreted as very unacceptable and 3 points as very acceptable. The SUS converts the participants’ responses into 100 points and substitutes them for the indicator to confirm satisfaction and overall usability (Fig. 2).

For usability testing, 3 scenarios were created, and 18 detailed tasks were included under them. Each scenario is divided into a pre-driving process (S1), a driving process (S2), and a post-driving process (S3) (Table 2). S1 and S3 were performed by the caregivers, and S2 was performed by the participants. Usability testing was conducted by establishing a testbed similar to the environment that can be experienced when moving in a wheelchair in the community. The testbed was aimed at testing the stages of the driving process (Fig. 3).

Table 2. Scenario for usability testing
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Fig. 2.
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Indicators of usability testing (RPE, DRS, ARS, SUS)

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Fig. 3.
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Wheelchair driving testbed

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2.5 Data Analysis

Analysis was conducted to evaluate the effectiveness, efficiency, and satisfaction of each detailed task performed using LPW1 and LPW2. Effectiveness was expressed as a percentage by calculating the successful proportion of tasks performed by each LPWs. To measure efficiency and satisfaction, average values and standard deviations of TPT, RPE, DRS, ARS, and SUS of each LPWs were calculated using Excel and then substituted into each evaluation index.

3 Result

Section 3.1 was written based on the results of scenario 2 to find out about the usability of users using LPWs. Section 3.2 was written based on the results of S1 and S3 to find out the usability in setting the LPWs by the caregivers.

3.1 S2 Tasks Performed by the Participants

3.1.1 Effectiveness

The effectiveness of the two LPWs was confirmed by analyzing the success or failure of the task. All participants succeeded in performing LPW1 except for one participant who did not succeed in performing T10. LPW2 was successfully performed by all participants at once in all scenarios. Thus, LPW1 showed 80% effectiveness and LPW2 showed 100% effectiveness.

3.1.2 Efficiency

TPT were averaged 11.5 s (LPW1) and averaged 6.2 s (LPW2). RPE scores averaged 9.7 points for LPW1 and 9.4 points for LPW2. Both LPWs were usable with very light effort. DRS scores averaged 1.3 points for LPW1 and 1.4 points for LPW2. Both LPWs were analyzed close to a barely easy level. (Table 3).

Table 3. Result of S2 TPT, RPE, DRS
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3.1.3 Satisfaction

ARS scores averaged 1.6 for both LPWs. Both LPWs were analyzed close to a moderately acceptable level. (Table 4). As a result of SUS analysis, LPW1 scored averaged 77.6 points (Black line), which was measured as grade B/’Good’ usability. LPW2 scored averaged 86.4 points (Red line), which was measured as grade A/’Best imaginable’ usability (Fig. 4).

Fig. 4.
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Result of S2 SUS (Color figure online)

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Table 4. Result of S2 ARS
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3.2 S1, S3 Tasks Performed by the Caregivers

3.2.1 Effectiveness

All caregivers performed successfully in all scenarios at once. Thus, LPW1 and LPW2 showed 100% effectiveness.

3.2.2 Efficiency

TPT were averaged 6.7 s (LPW1) and averaged 7.9 s (LPW2). RPE scores averaged 7.3 points for LPW1 and 6.7 points for LPW2. Both LPWs were usable with extremely light effort. DRS scores averaged 2.9 for both LPWs. Both LPWs were analyzed close to a very easy level.

3.2.3 Satisfaction

ARS scores averaged 3 points for LPW1 and 2.9 points for LPW2. Both LPWs were analyzed close to a very acceptable level.

4 Conclusion

Wheelchair users face a number of obstacles when traveling in a community environment. Through this comparative usability testing, the usability of two LPWs developed in Korea was examined from the perspective of users and caregivers. From the user’s point of view, the usability was investigated by driving in a driving environment that can be experienced when moving to the community using a LPW, and by setting the battery and cushion of the LPW from the caregiver’s point of view.

There was a difference between the two LPWs in terms of effectiveness and satisfaction in the participant’s driving, and there was no significant difference in efficiency. There was no significant difference between the two LPWs in the performance of the caregivers.

As a result of the usability testing, the usability of the heavier LPW2 was highly evaluated. This can be interpreted that users feel a sense of stability in the LPW with a certain amount of weight. In future studies, it is considered necessary to study the appropriate weight of LPW that users can feel stable.

This study has a limitation in that it did not include powered wheelchair users with various types of disabilities by limiting the subjects to people with physical disabilities. It is believed that future research needs to evaluate usability considering various types of disabilities. It is expected that this study will be used as basic data in future research on LPWs.