Usability of mobile applications: A conceptualization and instrument development study based on Apple human interface guidelines

Abstract

Smartphones and their services make people's lives much more accessible and enable them to use their limited resources more effectively. With the advancement in technology, the capabilities of smartphones have also increased, and several mobile applications have been developed. Through these mobile applications, people can perform and manage many activities, from making hospital appointments to financial transactions, communication, and educational activities. For instance, mobile e-government applications enable various public services to be performed with a single click with less physical effort. Being available at any time and from any location is one of the most important advantages of mobile applications. The portability of mobile devices and their suitability for a variety of user settings are important features for users. Users always expect to be able to seamlessly enjoy the service a mobile application promises to deliver. However, the use of mobile applications in a wide range of usage environments and some physical constraints, such as small screen sizes, are the factors that complicate usability studies for mobile applications. The ever-evolving nature of smartphones, in parallel with developed technology, also complicates the design of mobile application interfaces. All these difficulties and the continued widespread use of mobile applications have accelerated the studies related to mobile application usability. Initial studies on mobile application usability were derived from previous studies on website usability. However, the characteristics of websites differ from mobile applications in terms of the devices they are used and the usage environment. Therefore, the usability of mobile applications should be handled individually. In the literature, an essential part of the studies on mobile application usability focus on only one type of mobile application, such as mobile health, mobile commerce, and mobile learning. These studies are helpful in evaluating usability for a particular type of mobile application. On the other hand, this study provides a comprehensive usability model that may be used in the design and evaluation phases of any kind of mobile application by software developers. Furthermore, the developed survey instrument based on the mobile application usability concepts evolved may be used to understand the significant factors in the usability assessment of mobile applications from the users' perspective. In this study, a three-step formal methodology was used to conceptualize and develop a survey instrument: conceptualizing the constructs, developing the scale, and evaluating the measurement properties. In the first stage, the first matrix of open codes was created by examining Apple's human interface guidelines line by line, which was taken as the main source of the open and axial coding procedure for the conceptualization of constructs. This open code matrix, consisting entirely of qualitative data, was then examined eight more times and open and axial coding procedures were applied. The finalized matrix consists of 16 axial codes, 29 subcategories, and 92 open codes. Sixteen constructs are conceptualized, namely instant start, branding, orientation, collaboration, content, search, privacy, graphics & animations, realism, control obviousness & reliability, effort minimization, consistency & standardization, concise & user-driven language, feedback, navigation, and transition. In the second stage, an initial item pool consisting of 113 items measuring 16 constructs was created by making use of the open codes created in the previous section and the relevant literature. The initial version of the items was screened with a procedure. First, a face validity check was performed to eliminate vague items. Then the survey items were applied to real users with a pilot study, and a content validity check was performed to validate the items. As a result of analyses, 69 items representing 16 constructs were revealed to evaluate the measurement properties of the scale. At the final stage, the measurement properties of the developed survey instrument were evaluated with exploratory and confirmatory analyses. The factor structure was discovered with the first collected data (n1=476), and the discovered factor structure was confirmed with the second data collected with different participants(n2=583). The target audience of these survey studies is social media mobile application users, which is one of the most widely used mobile application types and appeals to a large part of society. In the exploratory analysis, two items with factor loadings lower than the threshold value were excluded from the item pool. Confirmatory analysis was performed with 67 items representing 16 constructs to validate the constructs and their corresponding items revealed with explanatory analysis. The internal reliability, convergent validity, discriminant validity and fit indices of the measurement model were examined, respectively. Finally, for the nomological validity of the developed scale, the fit indices of the structural model and the effects of constructs on satisfaction and continued intention to use were examined. The results show that the scale developed for mobile application usability explains a significant part of the variability in satisfaction and continued intention to use. In addition, the significant relationships between mobile application usability constructs and satisfaction and continued intention to use provide evidence for the applicability of the developed survey instrument.