. Understanding and Supporting Mobile Application Usage Dissertation zur Erlangung des Grades Doktor der Ingenieurwissenschaften (Dr.-Ing.) der Naturwissenschaftlich-Technischen Fakultäten der Universität des Saarlandes vorgelegt von Matthias Böhmer Saarbrücken, den 16. Juli 2013 Dean: Professor Dr. Mark Groves Head of Committee: Professor Dr. Philipp Slusallek Reviewers: Professor Dr. Antonio Krüger Professor Dr. Anind K. Dey Professor Dr. Albrecht Schmidt Committee Member: Dr. Ralf Jung Day of Defense: September 6, 2013 Notes on Style References to web resources (e.g., links to articles published on the Internet) are provided as URLs within footnotes with date of last access; longer URLs have been shortened. References to scholarly published resources (e.g., journal articles and conference proceedings) can be found in the Bibliography at the end of this thesis. When referring to unknown individuals in third person singular (e.g., users of a system or anonymous participants of a study) we alternate between the female and male pronouns between paragraphs for reasons of gender neutrality. Acknowledgements Over the last few years I have been fortunate to get into contact with the following people. They supported me in a variety of ways working on the document which you are — hopefully — just about to start reading. I am deeply grateful to Antonio Krüger for supervising my dissertation. He has shaped my way of thinking with fruitful discussions, while leaving me enough freedom to set out my own research agenda. I thank my reviewers Anind K. Dey and Albrecht Schmidt, who inspired my overall work early on with their own pa- pers and research in related fields. I am thankful that both eventually agreed to review my thesis. I thank Gernot Bauer for encouraging me to start working on a PhD, helping me with the first steps, and teaching me: Clarity is essential. I have always had the luck to work with nice people in pleasant and inspiring environments. Therefore I thank my former and current colleagues at DFKI in Saarbrücken, especially Benedict Fehringer, Florian Daiber, Johannes Schöning, Markus Löchtefeld, and Sven Gehring (in alphabetical order) who refreshed my brain cells not only with chitchat at the coffee maker, but also with challenging questions and a lot of fun. I thank Morin Ostkamp, Stefan Jürgens and Sven Luzar for being supportive colleagues during the first years of my work at Münster University of Applied Sciences. I am thankful to all people whom I had the pleasure to collaborate with over the last few years. Among those the coauthors who worked with me on the papers that this thesis is based on: Thanks for your input and discussion! I am especially thankful for the joint work with Brent Hecht and Luis Leiva — both fruitful collaborations resulted in parts of this thesis. Many thanks also to all students who I had the pleasure to supervise for their own theses, and who worked with me as student assistants. Also many thanks to Margaret De Lap for thoroughly proofreading my thesis. Finally, I thank my family for their support in all other matters over the years, and Dorothee: without you none of this would have been possible. Thank you for understanding and supporting me! i Für Doro und die Rabauken. iii v Abstract In recent years mobile phones have evolved significantly. While the very first cel- lular phones only provided functionality for conducting phone calls, smartphones nowadays provide a rich variety of functionalities. Additional hardware capabil- ities like new sensors (e.g. for location) and touch screens as new input devices gave rise to new use cases for mobile phones, such as navigation support, tak- ing pictures or making payments. Mobile phones not only evolved with regard to technology, they also became ubiquitous and pervasive in people’s daily lives by becoming capable of supporting them in various tasks. Eventually, the advent of mobile application stores for the distribution of mobile software enabled the end- users themselves to functionally customize their mobile phones for their personal purposes and needs. So far, little is known about how people make use of the large variety of applica- tions that are available. Thus, little support exists for end-users to make effective and efficient use of their smartphones given the huge numbers of applications that are available. This dissertation is motivated by the evolution of mobile phones from mere communication devices to multi-functional tool sets, and the challenges that have arisen as a result. The goal of this thesis is to contribute systems that support the use of mobile applications and to ground these systems’ designs in an understanding of user behavior gained through empirical observations. The contribution of this dissertation is twofold: First, this work aims to understand how people make use of, organize, discover and multitask between the various functionalities that are available for their smartphones. Findings are based on ob- servations of user behavior by conducting studies in the wild. Second, this work aims to assist people in leveraging their smartphones and the functionality that is available in a more effective and efficient way. This results in tools and improved user interfaces for end-users. Given that the number of available applications for smartphones is rapidly increasing, it is crucial to understand how people make use of such applications to support smartphone use in everyday life with better designs for smartphone user interfaces. vi Zusammenfassung Mobiltelefone haben sich innerhalb der letzten Jahre signifikant weiterentwickelt. Während erste Modelle lediglich Sprachtelefonie zur Verfügung stellten, ermög- lichen heutige Smartphones vielseitige Dienste. Technologische Fortschritte, wie beispielsweise GPS-Lokalisierung und berührungsempfindliche Displays, haben neue Einsatzbereiche für Mobiltelefone eröffnet, wie solche als Navigationsgerät oder als Fotoapparat. Doch nicht nur in Bezug auf die Technologie haben sich Mo- biltelefone weiterentwickelt, sondern auch in der Verbreitung ist die Anzahl der Geräte enorm gestiegen. Sie werden allgegenwärtig im täglichen Leben genutzt, da sie ihre Anwender bei verschiedensten Aufgaben unterstützen können. Das Auf- kommen von Vetriebsplattformen für die Verbreitung mobiler Software erlaubt es dem Anwender selbstständig Modifikationen an der Funktionalität seines Geräts vorzunehmen und dieses an persönliche Zwecke und Ansprüche anzupassen. Bisher ist wenig darüber bekannt, wie sich Anwender die Vielfalt zu Verfügung ste- hender Applikationen zu Nutze machen. Als Folge daraus gibt es bisher nur rudi- mentäre Unterstützung für Anwender, die Vielfalt von Applikationen effektiv und effizient einzusetzen. Diese Dissertation ist durch den Wandel des Mobiltelefons vom reinen Kommunikationsgerät hin zum multifunktionalen Werkzeug motiviert. Das Ziel dieser Arbeit ist es, Systeme für die Unterstützung einer besseren mobilen Applikationsnutzung zu entwickeln, deren Design auf dem neuen Verständnis von Benutzerverhalten beruht, das durch empirische Studien gewonnen wird. Diese Dissertation hat einen zweiteiligen Beitrag: Zum einen werden theoretische Erkenntnisse dazu erarbeitet, wie Anwender die Applikationsvielfalt nutzen, instal- lierte Applikationen auf ihren Geräten organisieren, neue Applikationen entdecken und zwischen diesen in der Ausführung wechseln. Die Erkenntnisse hierzu beruhen auf der empirischen Beobachtung von Nutzungsverhalten. Zum anderen hat diese Arbeit ingenieurwissenschaftliche Ziele dahingehend, die Anwender von Applika- tionen dabei zu unterstützen, ihre Smartphones sowie deren Funktionsvielfalt ef- fektiver und effizienter einzusetzen. Dieser Beitrag resultiert in der Beschreibung implementierter Systeme und verbesserter Benutzerschnittstellen für Anwender. Angesichts der rapide wachsenden Zahl zur Verfügung stehender mobiler Appli- kationen ist es wichtig, zu verstehen wie Endanwender diese nutzen, denn nur so kann die Nutzung von Smartphones gebrauchstauglicher und einfacher gestaltet werden. vii List of Publications Ideas, systems, applications, studies, data, results, conclusions and other text frag- ments as well as figures in this dissertation have in some cases appeared in the following papers. The chapters of this dissertation are partly based on these publi- cations. [40] Full paper: M. Böhmer and A. Krüger. A study on icon arrangement by smartphone users. In: Proceedings of CHI 2013 (appears in Section 4.3). [38] Full paper: M. Böhmer, B. Hecht, J. Schöning, A. Krüger, and G. Bauer. Falling asleep with Angry Birds, Facebook and Kindle: a large scale study on mobile application usage. In: Proceedings of MobileHCI 2011 (appears in Sections 3.2 and 3.3). [36] Full paper: M. Böhmer, L. Ganev, and A. Krüger. AppFunnel: A framework for usage-centric evaluation of recommender systems that suggest mobile applications. In: Proceedings of IUI 2013 (appears in Section 5.4). [183] Full paper: A. Parate, M. Böhmer, D. Chu, D. Ganesan, and B. M. Marlin. Practical prediction, prefetch, and prelaunch for faster access to applica- tions on mobile phones. In: Proceedings of UbiComp 2013 (appears partly in Section 3.4). [31] Note: M. Böhmer and G. Bauer. Exploiting the icon arrangement on mobile devices as information source for context-awareness. In: Proceedings of MobileHCI 2010 (appears in Section 4.2). [157] Note: L. Leiva, M. Böhmer, S. Gehring, and A. Krüger. Back to the app: the costs of mobile application interruptions. In: Proceedings of MobileHCI 2012 (appears in Section