An Evaluation Model for Measuring the Usability of Mobile Office Applications through User Interface Design Metrics

Usage of mobile devices and particularly smart phones has seen an enormous hike due to the advancement of mobile phone technology in recent times. People of different age groups, one way or the other, are now connected to different mobile phone applications, such as, Social Networking, Chatting, VoIP (Voice Over Internet Protocol) applications, Gaming etc. This rapid advancement has made it necessary for user interface designers of mobile applications to design user friendly interfaces for their applications, so that users can interact and use those applications with ease irrespective of their location. Usability plays a vital role for measuring the usefulness of such applications. After examining different experimental studies on usability assessment techniques imparted by various research workers, it has been determined that there is still a great deal of requirement where application designers have to guarantee more adept and improved usability of offline mobile applications, such as, Conversion Apps, offline encyclopedia, Translation apps, business use applications (office applications) etc. The primary objective of this study is to render a model for usability metrics of measuring the usability of office applications for smart phones. The effectiveness, usefulness and reliability of the proposed model is measured through two office applications named Office Suite Pro7 for Android and Office 365 for Windows 8 touch screen Smartphone.The results of usability testing and t-test show the significance of the proposed approach. The model in this study will enable the application designers to guarantee a more adept and enhanced usability of office applications for smart phones during the designing stage.


INTRODUCTION
U sability has always been a significant element that should be conceived for designing and developing any kind of application or product, particularly mobile apps [1][2]. With reference to ISO 9241-111998, usability can be outlined as: "The extent to which a product can be used by assigned users to accomplish determined objectives with effectiveness, efficiency and contentment in an intended context of use" (ISO FDIS 9241-210).

An Evaluation Model for Measuring the Usability of Mobile Office Applications through User Interface Design Metrics
Today, more and more users are being associated with different mobile apps, either online or offline, to make their daily life easier [3]. With reference to the statistics exhibited in [4], approximately 100 million users use office apps on their mobile phones for business and office work every day [5]. After interacting with these devices, users confront numerous issues, such as smaller screen size, navigation, input techniques, personalization issues and many more related to the advent of technology [6][7][8]. To get the better of such issues, the proper evaluation of usability on the basis of metrics for such devices is needed [2,[9][10][11][12][13][14].
Numerous studies have been conducted where the researchers have adopted and proposed a generic model, framework or technique for evaluating the usability of different kinds of mobile apps or systems (such as haptic systems) [15] and different online mobile apps (Hussain [10,16] that are already in use by number of users (already released) [9][10][17][18][19].
After analyzing these studies, it has been observed that majority of these models are restricted to the specific usability factors and cannot capture the specific usability problems associated with such applications. Moreover, a limited work is found for such applications in which specific features are measured and over all consolidated usability measurement is ignored. These limitations open the new usability perspectives for designing usability metrics model of mobile office apps.
The proposed model has a capacity to fulfill, not only user needs while using office applications but it also provides an ease while they interact with such applications.
The remainder of this paper is devised as follows: Section 2 provides relevant studies on usability, mobile phones and office apps. Section 3 talks about the suggested model along with its detailed description. Section 4, provides the research methodology. Section 5 describes the outcomes of the study and the last Section 6 addresses the conclusion and future prospects of the study.

LITERATURE REVIEW
Nowadays, as speedy development could be ascertained in media and applied science, an immense amount of incursion could be ascertained globally in the exercise of mobile phones as depicted in [3][4]. As a consequence of this monumental development, several people dwelling to various age brackets are being associated with mobile phones (either characteristic phones or smart phones) and its different apps [20]. Mobile apps can be outlined as those application systems which operate on mobile devices [21]. With the fast and developing requirements of mobile phones and its apps, several users are being engaged with different kinds of apps like financial apps, marketing and advertising apps, education apps etc. [20,22].
As a consequence of this speedy development, several research workers are being appealed for drawing out their researches addressing different usability skills pertaining mobile apps as summed up in Table 1.

Usability
Usability has always been a significant element that should be conceived for designing and developing any kind of application or product particularly mobile apps [1]. According to International Standard Organization (ISO 9241-11, 1998), usability of any product can be achieved through effectiveness, efficiency and satisfaction in an intended context of use.

An Evaluation Model for Measuring the Usability of Mobile Office Applications through User Interface Design Metrics
With the passage of time, several researchers have suggested different usability frameworks and standards comprising of various usability properties for multiple applications [1,13]. Walji et. al. [23] in his research, found that considering usability as an important element in designing any application provide benefits to both users as well the designers. From literature analysis it was found that user get frustrated, bored, disappointed if they did not feel ease to operate the software according to their needs [21,23,31]. Moreover, it was also found that majority of the usability studies are limited in covering the usability problems and did not cover the specific problem areas as detailed in Table 1.

An Evaluation Model for Measuring the Usability of Mobile Office Applications through User Interface Design Metrics
According to [10], it is important to consider usability as an important element when designing mobile applications.
While designing mobile applications, several restrictions are imposed like small screen size, navigational problem, input mechanisms, mobile personalization problems and new technological problems [7][8]. Keeping these problems in mind, it has become essential for designers to pay serious attention when evaluating usability of various applications, especially mobile applications.

Usability Evaluation for Mobile Applications
Evaluating usability of mobile application has always been a critical issue [19][20][21]. With the passage of time, several researchers have suggested different usability models related to mobile applications [1][2]13]. A number of such models for usability measurement are available for reference in Table 1. In Table 1 it is found that majority of the previous usability studies focused on individual usability evaluation or tool development of any specific application. Majority of these usability studies targeting either objective or subjective metrics individually. The testing procedure is also limited to novice or expert users.
Moreover, majority models are conceptual and not validated for any case study. These models cover only one or two usability factors with limited dataset. In literature, the researchers also pointed out different areas which needed to be addressed and improved by the usability experts for mobile applications.

Usability for Mobile Office Applications
From Table 1 it is found that there is a knowledge gap related to the improvement in usability evaluation models for mobile applications. With the wide spread usage of touch screen smartphones, users are demanding more usable and interactive applications, especially when it comes to business and office applications, like mobile office apps [4,20]. Various studies have been conducted to determine usability of office products like spread sheet, word processing for personal computers but a limited work has been found for mobile devices.
Venkatesh et. al. [32], in his research pointed out four major influencing factors (mobile devices screen size, resolution, input style and power consumption) which affect the mobile user experience during interaction. He suggested that improvements in these factors at the application level will enhance the user satisfaction level for such applications.
Moumane et. al. [6] presented two software quality evaluation frameworks for measuring the quality of mobile softwares. These frameworks are based on ISO 9126 standard and address mobile environmental issues like low bandwidth, limited storage capacities and limited user interfaces. They proposed that the frameworks need to be refined in terms of usability and maintainability.
Guirguis et. al. [33] have provided a smart model which facilitates the mobile user to access the web contents easily and smartly. The subjective metrics in terms of user satisfaction for the proposed model is collected from desktop and mobile devices. The authors suggested the need of more objective metrics need to be explored with high data set of participants.
Wogalter et. al. [34] in their research focus on the usability problems in word processing PC based applications. They focus on the feature characteristics of these applications.
At the end they stress the importance of usability and highlighted that poor usability would increase user attention, disturbance levels, consume more time and causes low productive word documents.

An Evaluation Model for Measuring the Usability of Mobile Office Applications through User Interface Design Metrics
Hussain et. al. [16] [36], and Attar [37] explorer usability through objective metrics. They explore usability with limited number of participants for specific application type (e.g. Spread sheets). Those researchers cover limited usability factors.
The literature review breakdown presented in Table 2 gives summary of research contributions towards usability metrics framework and major attributes of office applications. Metric) framework which hierarchically constitutes three steps described in [10,24]. The suggested usability metrics model comprises of following three layers.

Layer-1: Defining Content Based Usability Attributes for Smart Phones
In the first Layer, a new property namely "simplicity" has been imparted [10,24]. Reason behind adding this element is that after analyzing smart phone's guidelines published by [39], it has been observed that user interface should be developed simple in an attempt to enable users to interact comfortably with the application or system. As proposed by [11] it is imperative to develop simple user interfaces for enabling users to interact comfortably with mobile apps particularly with business and social networking applications.
So for such reasons, "Simplicity" property has been added in a usability metrics model along with other three properties outlined by [10,24]. There are some research workers who have assessed online office apps [12] and Microsoft Word apps being used on personal computer [17]. In this research paper, main focus is on assessing usability of mobile office apps. To assess these apps,   [6,[9][10][11][12]18]. Simplicity is evaluated by metrics: level to which users find it easy: to edit data, insert table, picture, chart and shapes, to recover from errors/mistakes while performing tasks and to timely discover how to perform a specific task [11,16].

An Evaluation Model for Measuring the Usability of Mobile Office Applications through User Interface Design Metrics
Efficiency: The second category of usability factors incorporates user's way of performing tasks in a given time constraint. Prior research asserted that efficiency sub factors like time behavior, features are the most important determinants of the measuring usability of mobile office applications [6,[9][10]16]. Efficiency is evaluated by metrics: The capacity of a system (application) to enable users to ably interact with the application's supported characteristics and complete specific assignments with precise and successful outcomes within the anticipated period of time [9,[11][12]40].  [6,[9][10][11][12]16,40].

Layer-2: Defining Sub Factors for the Defined Attributes
In this layer, sub components for the content based usability properties distinguished in previous layer regarding mobile office apps are outlined. These sub components are distinguished after studying different studies on usability assessment of various kinds of systems and application like Mobile-Wireless Information systems [19], online apps [12,41] and mobile apps [10,24,31].

Layer-3: Developing Measurable Criterion (Metrics) for Defined Sub Factors
Once the sub components have been outlined in layer 3, in this step, the standard (systems of measurement) for assessing these sub components are designed by critiquing the systems of measurement outlined in mGQM framework [10,24].
Except critiquing mGQM framework, different studies associated to usability metrics model and frameworks [9] for assessing various kinds of systems and application like Mobile-Wireless Information Systems [19], Webbased apps [40], Mobile apps [10,34] are also reviewed.
After reviewing all these studies, standard (systems of measurement) for assessing usability of mobile office apps is finalized. Once the standard is finalized, the questionnaire is developed keeping in mind the standard finalized for assessing mobile office apps. This questionnaire is developed on the basis of queries developed by [11]. Principal objective of designing this questionnaire is to assess the usability of mobile office apps by knowing user's comments and suggestions against every question developed on the basis standard outlined for such apps. The suggested usability metrics model for mobile office application is shown in Fig. 1.

RESEARCH METHODOLOGY
This section describes the material and methods used for the development and validation of the proposed model.
For designing the proposed model we empirically review the previous researches of usability and mobile applications especially mobile office applications.
Majority authors presented their models or frameworks in a hierarchal way [42][43] and structured their models by using mGQM approach [24,43]. For the construction of our proposed model we also adopted mGQM in which we

Usability Testing
There are several mobile apps that are installed on

RESULTS AND DISCUSSION
In the field of HCI (Human Computer Interaction), the researchers pointed out that design methods, frameworks, and models cannot be qualitatively validated [44]. And this statement can also be applicable for usability models too [45]. In literature, researchers validate their models through following key factors (1) identification of usability problems [42][43], (2) categorization of improvement areas [43] and (3)

CONCLUSION
In this research, a study has been carried out to assess the usability of office application being installed on smart phones. During this research, various studies pertaining to the usability assessment factors and frameworks for mobile apps have been critiqued in an attempt to incur the usability that are well-matched with mobile office apps.
After getting these factors, a collection of metrics (systems of measurement) has been designed for smart phones office apps in the form of Proposed Model.
The suggested model will facilitate users by enabling them to interact with more users' friendly office applications.