Mobile Methodologies: Experiences from Studies of Mobile Technologiesin-Use

Transcription

1 Mobile Methodologies: Experiences from Studies of Mobile Technologiesin-Use Alexandra Weilenmann Viktoria Institute, Sweden Published in Proceedings of the 24 th Information Systems Research Seminar in Scandinavia (IRIS 24), eds. Bjørnestad et al. vol 3, pp Abstract. The aim of this paper is to discuss methods for studying the use of mobile technologies. It is argued that many previous studies of mobility are limited in the use of data collection methods in that they use the workplace or other fixed setting as the location to study the mobile technology. In this paper, I relate and discuss experiences from three different studies of mobile technologies. These studies differed in several ways; in the technologies studied, the general field approach, methods for collecting data, the research question formulated beforehand, as well as the role of the researcher, and the extent of naturally occurring interaction. The practical implications of these differences during the fieldwork are discussed. 1 Introduction It has been estimated that within a few years, mobile computers in various forms will outnumber the personal computer. For those interested in design of information and communication technologies, as well as understanding their use and impact on society,

2 the increasing mobility of the technology one aims to study, causes difficulties. It is no longer enough to walk into an office and study the use of technology in there; a lot of the work is carried out outside the workplace in different, sometimes unpredictable locations. Furthermore, mobile technologies are not just a workplace issue. People s personal and private lives are also in focus. To a large extent, mobile technologies enable people to cross boundaries between work and other activities (Gant and Kiesler, 2001). This blurring of boundaries contributes to the challenge of studying mobile technology use. Within Computer Supported Cooperative Work and related fields, there have been a number of studies which rely upon or get inspiration from methods from social sciences, such as ethnography, ethnomethodology and conversation analysis. Among these are Lucy Suchman s Plans and situated action from 1987, the work by Heath and Luff (e.g. Technology in Action, 2000), and the recent collection of Workplace Studies (Luff et al., 2000) presents a number of studies where the authors to some extent focus on naturalistic interaction. Although there exists a growing body of work in this vein which focuses on the use of mobile technologies, there has not been much explicit discussion of the particular issues and problems raised when studying people and technology which are highly mobile. It is the aim of this paper to discuss how these methods can be applied to study the use of mobile technologies; more specifically the paper focuses on methods for data collection. As mentioned above, collecting data about the use of mobile technologies is difficult simply because the technology is mobile. The discussion is focused around three examples of studies of mobile technologies in which the author participated. These studies provide a basis for the discussion, as they are different in a few interesting way with regards to technologies as well as the setting, and thus the suitable practical methods for studying their use and deployment. The three studies differ in the general field approach, methods for collecting data, the research question formulated beforehand, as well as the role of the researcher, and the extent of naturally occurring interaction. Obviously, the choice of method is strongly coupled with the aim of the study. In this paper, methods are discussed as means to gain knowledge about the ways in which people use mobile technologies in their everyday activities. The studies had as a main goal to describe these ways, along with an attempt to extract findings useful when designing new mobile technologies. The goal with this paper is however to generally discuss methods for studying mobile technologies in use, and it is not discussed in detail how (or if ) these findings later can be applied. The paper starts off with a review of other studies of mobile technologies. After that, I present the three technologies studied. The differences between the technologies and what those differences imply for the choice of methods are then discussed.

3 1.1 Studies of mobile technologies related work Within the field of Computer Supported Cooperative Work there has been an emphasis on stationary settings. Often, the workplace in focus has been an office of some kind, a control room, a factory, etc. Sometimes mobile workers are studied, such as photocopier service personnel, but then the focus is not on their work as mobile people, and what that implies for their technology use, rather their work at these sites. With Hughes et al. Moving out of the control room (1994) and Luff and Heath s Mobility in collaboration (1998), came the move towards shifting focus. These were two of the first papers to be published within this field, which explicitly focused on the mobility of the workers and their technologies. However, since then, the increasing mobility of people and their tools, has received remarkable little attention within the field. In the CSCW 2000 conference, for instance, there were just three papers devoted to the theme mobility. In other fields such as ubiquitous computing, wearable computing, and to some extent human computer interaction, mobile devices have received much more attention. However, in these fields there are few studies of the use of these mobile devices; rather the research concerns ways to improve the technology in various ways which are sometimes not related to its use. Also, it is interesting that widespread, mobile technologies used by many people in their everyday lives, has received so little attention. I am thinking primarily on the VHF-radio, which is the main work tool for many mobile workers, and the mobile phone, which has become an almost ubiquitous tool in many countries. As regards to radio, there are few studies of its use and the characteristics of radio talk, as pointed out by Luff (2001). And the use of mobile phones has just recently received attention, as Brown (2001) also notices. This is not to say that studies of the use of mobile technologies do not exist. There are several fine studies of different aspects of mobile technology use, based on some sort of ethnographic fieldwork as well as on other methods. In many studies of mobile technologies, observations are combined with other methods for data collection to get all interesting and relevant aspects. For instance, Green, 2001, investigates the notion of surveillance with regards to mobile phones through combining interviews with observations. My main point is that many previous studies of mobility are limited in the use of data collection methods in that they use the office, control room or other fixed setting as the primary location to study the mobile technology. For instance, when interested in the mobile work of ambulance crew the research is carried out in the control room where the ambulances are coordinated rather than in the vehicles, and when interested in the work of airplane pilots the researchers go into the control tower. In this paper, I hope to show some ideas on how highly mobile people and technologies can be studied in the locations where the mobile activity is actually taking place.

4 2 Three Studies - Three Types of Mobile Technologies The discussion about method described here is based on three studies of mobile technologies-in-use. In the studies described here, the mobile technologies in focus were quite different, as well as the situations in which they were used. In this section, these differences will be outlined, in order to see how different technologies and use situations call for different data collection approaches. 2.1 A mobile awareness device The technology in focus here was a small mobile awareness device, called the Hummingbird. 1 The Hummingbird is a device developed to provide information of the presence (or absence) of other users, thus enhancing the awareness of other members in co-located groups. The form of awareness that is provided is awareness of the physical proximity of others. The idea is to provide mobile groups with continuous awareness information, something that earlier has been provided mostly for stationary use (e.g. ICQ). The Hummingbird was not designed to be used in a specific activity or to fulfill a certain goal. The purpose of the study was to evaluate the use of this device and to see how a group of users made sense of this new mobile device. The group selected to try it was a group of skiing instructors. The reason for choosing such a group was that the activities within a ski group provided an interesting, not always easily defined boundary between work and social activities. It was of interest to see how the devices were made at use in these different yet interrelated activities. The period during which the study was carried out was a clearly defined: the extent of the skiing trip. The instructors got the device at the day of departure for the mountains. They had not seen or heard much about the devices before this. This was a methodological point also, as one of the goals was to see how the instructors themselves made sense of the devices in their activities. 2.2 Mobile phones Although a widespread technology in parts of the world, the mobile phone has not until just recently received much attention from researchers. The motive behind the study 1 The Hummingbird was created by the PLAY research group. The prototypes used Nintendo Gameboy as a platform. A small radio transceiver communicated with the Gameboy through the serial port. The devices did not depend on an infrastructure, simply on the other Hummingbirds. When two or more Hummingbirds were within a distance of less than a hundred meters, the devices produced a sound they "hummed". At the same time, the name of the user appeared on the display, distinguishing the users. The names of the ski instructors were divided into two columns on the display: "here" and "away".

5 described here was a general interest in understanding the use of mobile phones among specific group in society, namely teenagers (Weilenmann and Larsson, 2000a,b, Weilenmann and Larsson, forthcoming). The project started out with a phase where focus groups and fieldwork was carried out at the same time (Larsson, 1999). From that study, we drew the conclusion that we could generate a lot more interesting data from more fieldwork, whereas interviews (reported use) would give us more information about needs, wants and opinions of mobile phones, rather than the actual use (Weilenmann and Larsson, 2000b). We therefore continued our studies in public places, focusing on naturally occurring interaction involving mobile phones. The fieldwork was performed in central Göteborg, Sweden. We focused on inner city public use of mobile phones among teenagers. The fieldwork was carried out in a wide range of places and situations, such as cafés, public transport (bus, tram, train), an amusement park, shopping malls, etc. In all these places, teenagers can often be seen passing time or hanging out. When beginning the field studies, the overall question was: What do teenagers do with mobile telephones? The question was quite general, as we did not want to make too many prior assumptions about the use, and by that miss out on what was really going on. When doing fieldwork on public transport, we would generally sit on a bus or tram and observe the use and handling of phones. In cafés, we would sit at a café table like other café visitors. In the other environments, the amusement park, the shops, on town, in all these places we tried to do what people in these places generally were doing 2. We did fieldwork during different times of the day and week, which means that the data encompasses late Saturday night, as well as early Monday morning, and everything in between. During our studies, our method for documenting our observation has been by making field notes. In these notes, we make detailed descriptions of all observable and hearable events that include teenagers using their mobile phones in any way. All the places where we did fieldwork are public. We have not studied mobile telephone use in the home or in other private settings. The reason behind focusing on public use was originally methodological: we wanted to be taken for any other participant, not as researchers focusing on naturally occurring interaction. This would not have been possible, had we chosen to study teenagers use of mobile phones in the home. 2.3 Radio and awareness displays The next field study to be discussed in this paper was carried out at Arlanda airport. It addressed the issue of attempts within air traffic management to invent new, innovative techniques to support not only air traffic control in the tower, but also engage pilots and 2 With the exception that we were making notes.

6 other vehicle operators in the coordination of activities. In a way this can be seen as an attempt to decentralize coordination. We studied a group of mobile ground personnel very important for air traffic management, namely those who keep the runways clear from snow. In the Arlanda airport, there is a risk of snow during half of the year, and a snow clearing team is during that time constantly ready to go out and clear the runways. The snow clearing of the runways has to be very quick, so as not to delay traffic, but at the same time they cannot take any risks. In the coordination of their work, the snow crew is aided by two types of mobile technologies one old and one new. The old technology was the UHFradio (ultra high frequency), and the new technology was called the SnowCard, a display showing the location of other snow vehicles. The snow crew uses UHF radio to communicate within the group as well as with the control tower. It is a simplex system, which means that it is only possible for a sender at time, but that everybody with radio equipment can listen. Apart from the UHF radio, some of the vehicles are also equipped with a display with a moving map. This is an application called SnowCard based on a new system concept. On a display presenting a map of the airports, a number of the sweeping groups vehicles are represented by small dots. When the vehicles move along the airport the dots follow. This is made possible by a positioning system in each vehicle and a digital radio communication link. All vehicles send out information on their identity and position, and all vehicles with the equipment can receive the data, presenting it on a map. The new display system was introduced with the intention to increase situational awareness to vehicle operators. It was our aim to evaluate the technologies available to coordinate the snow maintenance at the airport. In order to study the use of these technologies in the everyday work of the snow crew, we went out in the field. For a total of five snow clearance occasions, we went with the snow sweepers, sitting in their vehicles when they carried out their work on the runways and the surrounding areas. Most of the vehicles had an extra seat next to the driver seat, where the researcher could sit. We normally organized it so that one person always was in the front vehicle. Some drivers talked a lot with us and were interested in explaining their work and their use of the systems, whereas others did not take much notice of us. It enabled us to focus more on the work, and listen to the radio communication. During all this, we took extensive field notes. When in the vehicle with the snow sweepers, it was sometimes difficult to hear and comprehend the radio talk. In order to get the details of the ongoing talk, we made audio recordings. These were carried out during two days of the fieldwork. We placed the recording machine in the snow crew s control room, in a place where it was not disturbing their work. Due to the nature of the work, we had to wait for it to snow before going out with the snow sweepers. This meant that we spent a lot of time in the recreation room of the snow sweepers, in the garage, etc. That enabled us to talk to the

7 snow crew and get their opinions of their work situation, as well as getting a sense of the work place. 2.4 Summary of the studies Hummingbirds Mobile phones UHF Radio + SnowCard Technology Mobile, personal device Mobile, personal device Mobile technology attached not to a person but to a snow clearance vehicle Level of use, adoption Research question Data collection methods Number of people in the field Access to field, necessary preparations New technology, introduced as experiment for purpose of study General (How are the devices used) although aim was to evaluate the use, thus assuming that it would be used in some way. - Field work during the use; field notes. Not much questions in the field. - Focus groups after; recorded Widely adopted Very general How are mobile phones used in the everyday life of teenagers? Fieldwork in public places Field notes - Radio widely adopted, work relied on it - SnowCard - recently introduced, not widely adopted. Study set out to evaluate use. Original question how is the SnowCard system used? When it turned out it was not widely used, focus shifted to the other technology for carrying out work, i.e. UHF radio - Fieldwork - Asking questions in the field - Official Documentation - Recorded (audio) of interaction over radio One Two at the same time Two at the same time Had to identify group willing to test device Easy the field is out there - Difficult. Security aspects on airport. Misunderstandings in what sort of study we wanted to do. - Had to wait for snow Table 1. A summary of the three studies of mobile technologies discussed in this paper. 3 Mobile Methods As I hope to show in this paper, different technologies, and different types of activities and mobility, call for different types of approaches. In this section I will discuss these differences and what they imply.

8 3.1 Combining fieldwork with other data collection methods In a field situation with mobile users who are physically distributed, the observer s task is difficult it is simply not possible to be everywhere at the same time. Therefore, it can be worthwhile to use other methods as well. In this section, I will talk about the benefits about combining methods for data collection. Interviews When evaluating a technology, it is very common to use some sort of interview technique. Interviews allow the researcher to get the opinions and ideas from participants. Sometimes these participants have general experience with the type of technology in focus, sometimes they have tested a certain technology or prototype of for the purpose of the study itself. The latter was the case in my study of the Hummingbirds. The ski instructors had first used the devices for a week, and then we met to discuss their experiences in focus groups. Gathering the participants in focus group conversations after the field experience, letting them describe their views of what happened, makes it possible to gain some insight into situations to which it was impossible to attend. Another advantage with performing focus groups after having spent time in the field is that it is possible for the researcher to test his or her understanding of the situation. Also it is the other way around, in that "ethnography provides broader frames of interpretation in terms of which focus group details take on added significance" (Agar and Macdonald, 1995:78). Field study and focus groups are two methods that complemented each other excellently in this case. In combination these methods gave a varied view of the ski instructors use of the Hummingbird, as well as their own opinion of the device. In the study of mobile phone use among teenagers, we relied totally on observations, which sometimes was a shortcoming. Certain things are not possible to get at in a field study where no questions are asked. Some of the issues we were interested in could have been investigated further by using some sort of interview technique. For instance, it could be useful to ask why they use their friends phones when they have their own. However, these questions would have been particularly interesting to ask from the very same people we had observed, in connection to the particular instances in which the actual event in focus took place. Audio and video recordings Within conversation analysis and ethnomethodological approaches it is natural ot have recordings of the interaction to be able to analyze it in more detail. Video based field studies as are used among others by Heath and Luff (e.g. 2000) in order to focus on the use of a technology in a workplace.

9 In one of the studies discussed here, we set out to look at the details of the interaction, but without the aid of recordings. In the mobile phone study we collected our material ethnographic fieldwork, and documented our observations in field notes. This was sometimes a shortcoming. When analyzing the data, many times we lacked some crucial piece of information, which we could not remember, had not written down, or simply had missed. For instance, sometimes we wanted to know how and where the phone was placed on the table after using it, but had no notes of this. In order to do a more detailed and comprehensive study of how the phones were used in the interaction was carried out, we would have needed video and audio recordings. However, it is important to remember that it would have been difficult if not impossible to get audio and video recordings of the natural occurring action described here. Studying the use of such a highly mobile technology as the mobile phone, poses difficulty to the use of audio and video based analysis. It would perhaps have been possible in the cases where people were a little less mobile, such as the cafés, where we could have recorded a certain table, for instance. In other locations, e.g. the amusement park, we would have needed several cameras and microphones in quite a lot of places in order to collect as much material as we have done through observations. One possible solution would be to use mobile recording equipment instead of fixed, where the people observed can be followed around and recorded. This clearly raises many ethical concerns, at least when studying people in public settings. Having mobile equipment would imply that no specific place is used for collecting data, which makes it more difficult to inform people of where they might be recorded. Until these issues have been satisfyingly resolved, there is much interesting and useful data to collect through ethnographic observations. In relation to this, I want to stress the benefits of being two people in the field at the same time, which is discussed in the next section. In the study of the snow group, the fieldwork was combined with audio recordings of the radio communication between the snow crew itself, and between the control tower and the snow crew. One of the goals with the study was to investigate the use of radio, which made it necessary to look into the conversations in closer detail. These recordings made it possible for us to look at the details of the conversations, details we were unable to grasp when in the vehicles overhearing the radio. Furthermore, the recordings proved valuable when considering our field notes; many times the radio conversations clarified the situations we had gathered in our field notes. More generally, one of the difficulties with collecting recordings of mobile interaction is that the people in focus are moving about. The traditional way to get access to the field and do recordings, that is to ask a manager or the participants if it is okay to do recordings, is no longer valid when the aim is to study mobile people who might only be in focus a few seconds, and then move on as new people come into the field. This is true when studying public use of mobile technologies, and is probably one of the reasons why there are few field studies of such settings.

10 3.2 Collaborative fieldwork In two of the studies described in this paper, we were two researchers in the field at the same time. Doing collaborative fieldwork can be a great benefit when studying mobile technologies. The main benefit with doing collaborative fieldwork in a mobile setting is that it makes it possible to get different perspectives on the same situation. For instance, in the study of the snow crew, we placed ourselves in different vehicles. On one occasion, I would sit in the front vehicle (whose driver was responsible for radio contact with the control tower) and the other researcher would sit in the brake vehicle (whose driver was responsible for testing and reporting the friction and level of iciness on the runways). On other occasions, one of us would sit in the front vehicle, and the other further back in the line of snow clearing machines. This made it possible for us to get observations from different positions in the overall system. Also, the drivers of these different vehicles had different responsibilities, opinions and experiences, which they would often talk to us about. Note that being several people in the field at the same time is not substitutable to being several people involved in the project. The point is to actually be more than one person in the field at the same time. However, when data is collected in audio and video, this is somewhat different. This type of data makes it possible for several project members to look at more raw data when analyzing it. Also, another point with being more than one person in the field, and something which is true not only for mobile settings, is that it is possible to observe and take note of more details of the ongoing interaction. 3.3 The role of the observer The studies also differ in the general field approach, in that the researcher had a different role. This also meant that there were differences in the ways of getting access to the three studies. In the study of the ski instructors use of the Hummingbirds, I got access through a friend who was one of the instructors. When he liked the idea of trying the devices, he talked the others into doing it as well. In that way, I got a member of the group to negotiate my access. My role during the actual ski trip and the testing of the devices was quite peripheral. I did not ask them a lot of questions about their work or their use of the Hummingbirds. This was because I wanted the users to form their own opinions about the devices. This approach turned out to be successful. In the study of the snow crew at Arlanda airport, we had some difficulties getting access to the field. Arlanda is a large organization, and we were sent to several people before we found someone who realized that when we wanted to do fieldwork we actually meant that we wanted to go with the snow crew in their vehicles when they were doing their regular job. First, they thought it would be enough for us to do

11 interviews of the snow crew. Since our main explicit motivation between our study was to evaluate the use of the SnowCard system, we very soon became the people who are here to look at the new technology, in the eyes of the snow crew. Since some of them thought that the technology was a failure, it became difficult for us to get them to understand that this was not the only thing we were interested in. When in the actual field with the snow crew, different members took different notice of us. Some of them did not speak at all with us; they went on doing their job. Others were very interested in talking to us, and wanted to explain the ways in which they carried out their work and what they thought about the technology. This was a good combination. The field approaches described so far differed in that the phenomenon to be studied could only be studied in a certain place, with certain participants. This is a different type of field approach compared to when you study behavior in public places. The mobile phone study was differed from the others in that the phenomenon we wanted to observe was easily accessible in many public spaces. We did not make ourselves known to the people we studied; rather we were anonymous observers. Being an anonymous observer in a public space has interesting methodological implications. When looking at the local social impact of the telephone use, it is quite useful that the researcher only has access to the same information that the other participants have. For instance, if we are sitting on a bus and someone gets a phone call, we are in a similar position as other people on the bus, in reacting to the phone call. The ongoing interaction is as observable to us as it is to any other person currently present. This also means that we can only gather data that the members themselves actually make available; we felt that was good for ethical reasons. If someone talking on the phone did not want anyone in the surroundings to hear, we assumed they would simply talk quieter, making it impossible for us to hear, or choose not to have the conversation at all Observing non-use negative cases When in the field, it is sometimes tempting to draw too strong conclusions about the extent of use of the technology one is aiming to study. This is natural, since the explicitly formulated goal of the study is to see how the device or technology is used, and if it is not used to a large extent, one can easily be disappointed and over-interpret the few instances in which it is used. In this section, I want to argue the value of taking a closer at situations where the technology might have been used but was not for some 3 Another note on the ethics of this study: in reporting our observations, all the material has been anonymized. We do not use any names that we have heard. We only describe the teenagers with an approximate age, from our estimations. Further, the place and time in which we made the observations are described in a general manner only, which should make it difficult to identify any single person.

12 reasons, what I call non-use. It is an observation about something which is not happening. Looking into these reasons could give a lot of information about the technology and how it could be improved to be more useful. For instance, when I set out to study the use of the Hummingbird, I wanted to study the use of the device, but technological difficulties lead to limited actual use of it. This made me disappointed at first, but I soon realized that the study was not at all wasted because of this. Instead, I had a great opportunity to study the negotiations around the Hummingbirds use. Also, in trying to understand why the devices were not use I could get ideas of how to improve it. Similarly, when in the field focusing on mobile telephone use, it is important not to forget to look at situations where the mobile telephone is not used. It is easy to focus so much on use situations, that evident and interesting situations where the phones are not used are avoided. I argue that the non-observations are interesting because they can give information about in what situations the phones are not used or not present or not made visible. These instances have to be understood, in order to get the full picture of mobile telephone use among teenagers. Furthermore, in the study of the new awareness display in the snow vehicles at Arlanda, the same thing occurred. We set out to study the use of these devices, and even though we had an interest in the radio as well, the display was in focus initially. For one thing, the official reason for us doing the study there, and consequently the reason which we told the snow crew when they asked us about our purposes, was to study the use of the new display. Pretty soon we realized that the display was not a big part of their work. Instead the radio and the glancing and looking out the window to get information about the other s whereabouts, formed the basis of their collaboration. In a way, the non-use of the displays, opened up for possibilities to think about the reasons for the limited use of the new device, and how it could be improved. What information could they not get from the display that they seemed to need and got through the other resources? The answers to these questions sprung out of our observations of the nonuse of the display, in combination with observations with the observations of the use of the other resources. 4 Conclusions In this paper, I have discussed a few solutions and ideas on how to carry out studies of mobile technologies. It was argued that one way of getting a fuller picture of mobile technology use is to combine several methods. A combination of field observations with some sort of interview technique makes it possible to get information about situations where the researcher could not make observations due to the mobile situation. Another way to get better data of mobile use is to be several people in the

13 field when doing a field study. This way it is possible to get different perspectives of the situations. Further, another question that was discussed was what role the observer should take. Should it be passive and not asking questions, even covert, or should it be an open observation, where the research interviews the participants as the activity enrolls? This also ties in with how access to the field is gained, and how the motive behind the study is explained to the people in focus. Finally, it was argued that situations where the technology not was used could give information about what is missing, and give valuable information for new design. If one only focuses on the situation where technology is actively used, one can miss out on interesting things. When technology is used in ways one did not think beforehand, there might be interesting information to get. Traditionally, researchers in the field of computer supported cooperative work have focused on the work in stationary settings, such as offices, factories and control rooms. I have argued in this paper that many previous studies of mobility are limited in the use of data collection methods in that they use the fixed setting as the primary location to study the mobile technology. In this paper, I hope to show some ideas on how highly mobile people and technologies can be studied in the locations where the mobile activity is actually taking place. As technology becomes more mobile and aims at supporting people who are mobile, it is no longer enough to find a setting where this technology is in use, it is also important to grasp the very mobility of the activity, people and technology in focus. This poses a challenge to methods used when doing such studies. 5 Acknowledgements I wish to thank those involved in the studies described in this paper. I am especially grateful to Oskar Juhlin whom I worked together with in the Arlanda study, and Catrine Larsson with whom I studied mobile phone use among teenagers. Thanks to the anonymous reviewers and colleagues for comments which helped improve this text. References Agar, M. and Macdonald, J. (1995) Focus Groups and Ethnography, in Human Organization, Vol. 54 No. 1, pp Brown, B (2001) Studying the Use of Mobile Technology, introduction to Wireless World: Social and Interactional Aspects of the Mobile Age, Brown, B. N. Green, and R. Harper (eds) Springer Verlag: London. Brown, B. N. Green, and R. Harper (eds) (2001) Wireless World: Social and Interactional Aspects of the Mobile Age, Springer Verlag: London.

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