Usability is the extent to which a product can be used by specific users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use. The Nielsen’s usability model has been popularly used for system usability evaluation. This thesis introduces a modification to Nielsen’s usability evaluation model which was used to evaluate the usability status of digital libraries in tertiary institutions in Lagos State. The digital libraries used were that of University of Lagos, Lagos State Polytechnic and Federal College of Education, Akoka. This modified model incorporates four traditional attributes (Efficiency, Effectiveness, Satisfaction, Learnability) and two additional attributes (Discoverability and Cognitive Load) introduced by the researcher; these two attributes were introduced because they have been proven to be user centered attributes which will help in getting the users’ personal experience while using the software (digital library) unlike the existing usability evaluation models which were majorly system centered.
The digital libraries will be assessed using modified heuristic think aloud method. The study employed purposive sampling technique to select the three tertiary institutions that was used for the evaluation while Yaro Yamani formula was used to calculate the users’ population sample size of (40) for each of the institution. Six task based questionnaires were used to carry out test in collecting data for the study; they include: (i) Discoverability test, (ii) Cognitive Load test (iii) Learnability test (iv) Effectiveness test (v) Efficiency test and (vi) Satisfaction test. The mean of each of the usability attributes were used to evaluate the usability status of the digital libraries of the selected institutions. IBM SPSS statistics version 21 was used to calculate the mean.
The result of the usability test carried out established that the digital libraries of the tertiary institutions in Lagos state were usable. It also indicated that the users of the digital libraries were satisfied with the use of the digital libraries in the investigated institutions. For the three institutions, discoverability has a mean of 14.65, cognitive load has a mean of 14.81, learnability has a mean of 16.21, effectiveness has a mean of 16.89, efficiency has a mean of 16.56 and satisfaction has a mean of 16.27. Usability results of the evaluated libraries showed that the digital libraries are: Effective, Efficient, Satisfactory, helps users to learn and the discoverability and cognitive load of the students are fast.
In conclusion, this study has successfully modified the Nielsen’s usability evaluation model by adding Discoverability and Cognitive Load to its constructs and this study has also contributed to literature. The modified Nielsen usability evaluation model is recommended for use to evaluate usability of other digital libraries in other tertiary institutions in Nigeria and Abroad.

Title Page

Chapter One:  Introduction
1.1               Background to the Study
1.2               Statement of the Problem
1.3               Objective of the Study
1.4               Research Questions
1.5               Significance of the Study
1.6               Scope of the Study
1.7               Methodology
1.8               Operational Definition of Terms
1.9               Organisation of Subsequent Chapters

Chapter Two:  Review of Literature
2.0               Introduction
2.1               Definition of usability
2.1.1            Attributes of usability
2.1.2            Importance of usability
2.1.3            The role of usability in digital libraries
2.2               Usability Evaluation Models
2.2.1            Usability in ISO 9126
2.2.2            ISO/IEC 9126-1
2.2.3            Usability in ISO 9241
2.2.4            ISO 9241-11
2.2.5            Dix et al usability evaluation model
2.2.6            Nielsen usability evaluation model
2.2.7            Eason usability evaluation model
2.2.8            Enhanced usability evaluation model
2.2.9            Normative usability evaluation model
2.2.10          Modified Nielsen’s usability evaluation model
2.3               Usability evaluation methods
2.3.1            Card Sorting
2.3.2            Open card sort
2.3.3            Closed card sort
2.3.4            Cognitive walkthrough
2.3.5            Focus group
2.3.6            Think aloud
2.3.7            Contextual Inquiry
2.3.8            Heuristic evaluation
2.3.9            Questionnaire  
2.4               Digital library
2.4.1            Role of digital library in Education
2.4.2            Sources of digital library
2.5               Review of closely related work on usability evaluation  

Chapter Three: Methodology
3.0               Introduction
3.1               Research Design
3.2               Population
3.2.1            UNILAG digital library
3.2.2            FCE. (T) Akoka digital library
3.2.3            LASPOTECH digital library
3.3               Sample size and sampling technique
3.4               Usability model design/development
3.5               Method of data collection
3.5.1            Think Aloud
3.5.2            Heuristic evaluation
3.5.3            Modified heuristic think aloud method
3.5.4            Modified heuristic think aloud evaluation
3.6               Evaluation Tool
3.7               Tasks in Usability Testing

Chapter Four: DATA ANALYSIS, Results and Discussion of Findings
4.0               Introduction
4.1               Results of Usability Tests
                        Research Question One
4.1.1            Discoverability Test
4.1.2            Cognitive Load Test
4.1.3            Learnability Test
4.1.4            Effectiveness Test
4.1.5            Efficiency Test
4.1.6            Satisfaction Test
                    Research Question Two

Chapter Five: Summary, Conclusion and Recommendations
5.1               Summary
5.1.1            Summary of Findings
5.2               Conclusion
5.3               Recommendations

1.1 Background to the Study
The world has become a global village where information technology is used in all spheres of human activity to record, store, and disseminate information in the digital form. The new generation whose demand for information is insatiable is always demanding that traditional libraries be developed as a well-equipped and interconnected as digital libraries. Information and Communication Technology has revolutionized the concept of libraries such that libraries are gradually becoming digitized. A digital library comprises digital collections, services and infrastructure to support lifelong learning, research, scholarly communication as well as preservation and conservation of our recorded knowledge. It is also a process of democratization of information.

According to Arms (2012) a digital library is a managed collection of information with associated services where the information is stored in digital format and accessible over a network. A digital library is an organized collection of digitized material or it’s holding in the digital form, which can be accessible from digital devices on the network using Transmission Control Protocol/Internet Protocol (TCP/IP) or other protocol. In digital library high speed optical fiber are used for Local Area Network (LAN) and the access is over Wide Area Network (WAN) and provide a wide range of Internet based services including audio and video conferencing and others. Lynch (2013) opined that digital libraries provide users with coherent access to a very large, organized repository of information and knowledge.

According to the Berkeley Digital Library Project, University of California (Wilensky, 2012), the digital library will be a collection of distributed information sources. Some of the requirements for digital libraries are: Audio visual (T.V, V.C.R, life theatre and D.V.D), Computer, Network connectivity, Printer, Scanner, Storage devices, Software. Digital libraries have features such as: Incorporating learning and access, provides fast and efficient access to information, with multiple access modes, collections which are large and persistent over time, well organized and managed. The purpose of Digital Library is to expedite the systematic development of procedures to collect, store, and organize information in digital form, promote efficient delivery of information economically to all users, encourage co-operative efforts in research resource, computing, and communication networks, strengthen communication and collaboration between and among educational institutions and take leadership role in the generation and dissemination of knowledge. Digital libraries are getting famous for flexibility of use and more users can be facilitated at a time. As numbers of users increases, some issues relevant to interaction also arise while using digital libraries interface and utilizing its e-resources.

Usability is an important aspect of evaluating applications. Usability standards should be followed by the websites designer that supports user’s confidence level and interest when interacting with the website. Interactivity is a basic principle underlying the satisfactory behavior of the system by the user. System constraints are basic conditions to operate functionalities that integrate different services and sources in one interface that displays to develop interest of users. Searching of information is an important perspective where usability is of high relevance for user satisfaction. The interface is an important part in every system because this is the part where the user directly interacts with the system and utilizes services offered by the system. In every system, usability is a reverse procedure which means it can be done at any phase of software development life cycle. Specifically, students, teachers and researchers are end users of the application and their interaction with the system shows the satisfactory behavior. It helps developers or service providers to understand how the application is used by the end users and if the system is fulfilling user requirements or not. The best way to achieve this understanding is to repeat a usability test after a period of time because it requires a lot of changes to be made in the system, and for some users those are not satisfied with the functionalities or interactivity with the system sources. Therefore, usability testing is becoming an important ingredient in different types of application.

The International Standards Organization (ISO) (2014) defines usability as "the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use"(p.10). Nielsen (2013) points out that usability has five attributes: Learnability, efficiency, Memorability, low error rate or easy error recovery, and satisfaction. Brinck, Gergle, and Wood (2012) share a similar perspective that usability is functionally correct, efficient to use, easy to learn and remember, error tolerant,  and subjectively pleasing. In addition, Booth (2013) outlines that usability has four factors: usefulness, effectiveness (ease of use), Learnability, and attitude (likeability). Hix and Hartson (2013) classify usability into initial performance, long-term performance, Learnability, retainability, advanced feature usage, first impression, and long-term user satisfaction. The definitions given by ISO and Nielsen are most widely cited. Usability is about:
1.       Effectiveness - can users complete tasks, achieve goals with the product, i.e. do what they want to do?
2.       Efficiency - how much effort do users require to do this? (Often measured in time)
3.       Satisfaction – what do users think about the products ease of use?
The factors listed above is affected by:
1.       The users - who is using the product? e.g. are they highly trained and experienced users, or novices?
2.       Their goals - what are the users trying to do with the product - does it support what they want to do with it?
3.       The usage situation (or 'context of use') - where and how is the product being used? (ISO 9241-11, 2012).
 Usability is used to evaluate the digital library. Usability is important because any product or system is finally dependent on users who are to evaluate it. The digital library must pass the usability test. The existing usability evaluation models have been used to evaluate digital libraries abroad. It has been considered necessary to modify model from the existing model that can meet the peculiar needs of digital libraries in Nigeria.

1.2 Statement of the Problem
System usability and system usefulness are interdependent properties of system interaction while in combination, determines system satisfaction and usage. Most usability evaluation models such as the Nielsen model, ISO model and Dix model are majorly system centered, since digital libraries are to be used by individuals there is a need for a model that is both system-centered and user-centered. Many higher institutions in Nigeria provide academic digital libraries and usability evaluation have been conducted in some of these digital libraries; however, usability evaluation has not been conducted in UNILAG, FCE(T) and LASPOTECH digital Libraries to gauge the performance of the system in context of users’ perspectives i.e. how far the academic digital libraries fulfill the users’ needs.

Also, there is a need to know if the systems are useful to its users. Since digital libraries are supposedly designed for people (as users) to use, evaluating the performance of the system is of utmost importance. Therefore, this work develops a modified evaluation model for evaluating digital libraries and will be tested by end-users (students).

1.3 Objective of the Study
The main objective of this study is to propose a modified usability evaluation model and implement it using a digital library. The specific objectives are to:
1.      modify Jacob Nielsen usability evaluation model;
2.      test the model developed in (i) using three (3) digital libraries and
3.      bench-mark the model against Nielsen Usability evaluation model

1.4 Research Question
1.      What is the usability status of a given digital library using the modified model?
2.      Using the modified model, how acceptable is the model developed?

1.5 Significance of the Study
This research work is considered significant as it would modify Nielsen’s usability evaluation model that would be used for usability evaluation of digital libraries. Through this research work, we would know how acceptable the model developed is and the factors that contribute to the usability of digital libraries. These factors would help us when laying down the prototype of the digital library. Information provided would be credible, reliable and useful to enable the incorporation of results obtained into decision making process of the professionals, institutions and programmers in designing and improving their digital libraries. We can also give suggestions to government, education planners and school administrators on how to improve digital libraries to meet up to standardized digital libraries. The result of this research can help programmers, professionals and academic institutions in building standard digital libraries for their respective institutions.

1.6 Scope of the Study
The scope of the project is to modify Nielsen’s usability evaluation model that will be used to evaluate usability status of digital library in any tertiary institution in Nigeria. The research also uses the developed model to evaluate the usability status of a digital library of a tertiary institution. The developed model would be tested at the University of Lagos digital library, Federal College of Education digital library and Lagos state polytechnic, Ikorodu digital library and the following usability constructs (discoverability, cognitive load, efficiency, effectiveness, learnability and satisfaction) would be used to evaluate the digital library.

1.7 Methodology
We are modifying Nielsen’s usability model and it would be used to test the usability of a digital library. To achieve this, we will be using the modified Heuristic-Think aloud method.

1.8 Operational Definition of Terms
The following terms are defined as used in this study.
Usability: It is defined as the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified extent of use.
Digital library: A digital library is a collection of information and digital contents that are kept in digital formats and these are accessible to different users through computers by having access to the internet.
Internet: The internet is a global computer network that provides a variety of information and communication facilities, consisting of interconnected network using standardized communication protocols.
Modified model: It includes a combination of latent and observed variables. It allows you to integrate all available knowledge into one approach will reducing effort and maintaining accuracy.

1.9 Organization of subsequent Chapters

The chapters are organized in the following order. Chapter One contains the discussion on the general area covered by this research, the Chapter Two provides specialized overview of the literature review, Chapter Three describes the methodology used for this research work, Chapter Four contains the result and discussion of findings and Chapter Five contains summary of the work done, provides conclusions and recommendations.

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