This paper describes an innovative project (MoMEd) to evaluate mobile learning in clinical medical students. The conceptual model in Figure 1 shows the contribution of repetition and contextual learning theories to the process of mobile learning [15, 16]. The development of abstract problem-solving schema requires the "repeated active application of the knowledge acquired" which is enabled by the PDA . The instant access to information whilst in the clinical setting gives the students a better framework for understanding and storing the new information, and allows more efficient retrieval for future use . The 'just in time' experiences related by our students is as described by 'reactive' or 'opportunistic' learning . This is learning that is both intentional but "occurs in the middle of the action" rather than time being set aside for deliberate acquisition of knowledge, an apt description of the learning offered using the PDA.
Our model demonstrates how contextual factors can impact upon the learning process. Resources on the PDA were seen as a useful additional tool for them to have- a supplement rather than a replacement for their traditional learning strategies. This aligns with the theory of a learning ecology, an environment composed of a diverse variety of learning options, allowing each individual student to find the opportunity to access learning that addresses their own personal and immediate needs . Appropriation in which users not only adjust the tool to best fit their activities, but the tool may also cause the user to change their behaviour to accommodate using the tool effectively, was also seen . Home use of PDAs should also be seen as valid and part of the learning environment in mobile learning, with users able to access knowledge in different ways (PDA, book, personal computer) depending on the type and complexity of knowledge required. This finding also fits with the increasing popularity of tablet computers to access resources and the internet that are also available on home personal computers.
Both intrinsic mechanisms and external conditions may influence the learning possibilities available to a student . As described in activity theory, the social context is important, with "social rules and conventions govern[ing] what is acceptable" and attitudes influenced by surrounding opinion . Linked to this is the concept of acceptability of technology. The TAM model (Technology Acceptance Model)  suggested that usage of a system depended on several factors including perceived utility and ease of use that would determine the attitude towards technology and intention to use it. Holzinger  also suggested that previous exposure to technology and unobtrusiveness were also important factors that would affect acceptance and use of a technology. All respondents to our surveys had a personal computer and 38% already had another mobile device, suggesting that previous exposure was not a barrier to acceptance. The physical obtrusiveness of the PDA reflects the experiences of our students with respect to their concerns regarding teacher and patient opinion, and of a perceived failure to engage in the clinical moment, leading to potential inhibition of PDA use despite accepting its utility. This constrained their optimal use of the PDA. Alsos found that use of the device consumed the physician's attention, with poor action-transparency and inhibited patients from asking questions and raising issues . Houston et al in contrast found that the majority of their patients had positive attitudes towards handheld computers, although the clinicians themselves had reservations .
With sufficient support these barriers can be overcome, but a need for change was paramount, from the student's own attitude and behaviours to that of the clinicians and patients. This was achieved through communication by the students of the authentic learning nature of the tool, and by encouragement by the clinicians. Guidance on etiquette was required, so-called "mobiquette" . Institutional support helped both with encouragement and technical support, the importance of which has been highlighted by others [7, 27]. Becoming a more formalised part of the curriculum may aid this.
There are some important learning theories that we were unable to demonstrate directly, but this does not mean that they do not contribute. Rather it is due to limitations of the research tools available. Experiential learning with reflection  is likely to have a key role as shown by the broken arrows in Figure 1, and further research to elicit this would be invaluable. We were also unable to demonstrate that learning that occurred affected the students' actual practice. Extending the methods of data capture along ethnographical lines may allow exploration of these but this is difficult given the very nature of mobile learning which is spread across many contexts and over long periods of time . It makes it difficult to predict when a learning opportunity is likely to occur. Options include voice recordings or blogging, which may be more contemporaneous, or structured diaries have been used successfully . An ethnographic approach would also allow assessment of the effect on student-teacher and student-patient interactions that a move to a smartphone platform may have, and to find how the students and patients find ways to manage this.
The strengths of this study are that a large cohort of UK medical students were engaged on whom both qualitative and quantitative data were collected on use of PDAs as learning tools in a clinical setting in the UK. Provision of the PDA and software enabled us to involve students beyond a small self selecting group keen on technology,so reducing bias.
There are limitations to the study. The surveys and focus groups were dependent on personal reporting and so subject to recall bias, and the quantitative tracking data was too limited to offset this. The focus groups may have had an inherent bias in that those who chose to participate had engaged more with the technology. Purposive sampling could have been used instead to reduce this. The survey response rates were lower than ideal leading to non-response bias, potentially limiting the generalisability of results. However triangulation of qualitative and quantitative results showed consistency and suggest the findings are valid. Information from the final year group would have been useful but were not surveyed as they were sitting their final examinations prior to graduation. The usage tracking developed for this study was limited in that it only showed the number of times a resource was accessed and relied on students synchronizing their PDA with a personal computer, which not all students did despite regular requests from the project team. Ideally, time of day, location and duration of resource use would have been useful data to collect, with automatic uploading of usage data through a wireless network, and this has now been developed for use in DrCompanion for smartphones. The project was pragmatic in that it gave the same device and resources to all students.
Guiding future policy: research and resource design
Our research, although historical, has important lessons both globally as well as locally. PDAs are cheap and portable compared to standard computers, allowing use in rural and developing locations, and within the clinical setting. Although technology has advanced rapidly since this project began, the lessons from our research may be applied to settings in which the PDA may not be superseded for many years, and also to help to inform the emergent use of Smartphones. Smartphones may offer an advantage over classical e-learning as in many developing countries mobile telephone networks are a common alternative to networked computing . A further argument for progressing down the smartphone route were the problems encountered with the now old and slow user interface and the necessity of carrying two devices. However the concerns regarding the acceptability of a mobile device by staff and patients may be exacerbated by using a smartphone platform, as a few students recognized. Ideally, the transfer from a PDA to smartphone approach could have been carried out earlier, however the institutional investment in buying and supplying PDAs to students, the length of the contract with MedHand International and the lack of availability of a reliable smartphone platform for DrCompanion until late 2010 led to a decision by the project team to continue with the approach described in this paper.
Arguments against the widespread introduction and integration of mobile technology within medical education include the lack of hard outcomes showing that learning is improved, and the expense of such a project. There are the obvious costs for the initial outlay for the devices and the licensing, but also the less easily recognised costs of providing technical support and repair costs. We have demonstrated that only a proportion of students make use of their device so it may be seen as a waste of resources providing them to all. An opt-in programme may be a feasible substitute but whatever strategy is employed, there needs to be equity among students. New software is now developed for smartphone use that allows additional information to be collected including time of access, duration and nature of viewed content to the level of page of particular resource and information will be sent automatically and directly to a secure server over a wireless internet connection. This will give useful information to investigate relationships between situational context (home, hospital, university)and resource use.
In addition to altering the delivery platform, the resources on offer to the students could be developed further. Integration with other aspects of the medical school's e-learning facilities could be considered, such as an online question bank and an e-portfolio. This has proved successful for the ALPS project already .
The resources supplied on the PDAs were versions of existing paper and online publications optimized as much as possible for a mobile platform. I n transferring or developing resources for future mobile platforms such as smartphones and tablets, design is important and relevant to medical education where use of the mobile resource occurs in environments where information is required quickly but also where access may be interrupted at short notice and continued at a later time and maybe a different location. Content also needs to be adjusted so that it can be easily viewed on a small screen (chunking) and minimizes the potential for the user to lose or give up on accessing information due to navigation issues. Resources also need to be able to work effectively on multiple hardware platforms that will have an impact on development costs [2, 32].