How older adults meet complexity: aging effects on the usability of different mobile phones M ZIEFLE* and S. BAY Department of Psychology, RWTH Aachen University, Germany In this experiment, older and younger novice mobile phone users were examined when using handsets of different complexity. The independent variables were user age (young: 20 – 35 years; old: 50 – 64 years) and cognitive complexity of two mobile phones (Nokia 3210; Siemens C35i). The cognitive complexity of the phones was defined by the number of production rules applied when processing the four experimental tasks. Dependent variables were effectiveness and efficiency as taken from user protocols and the reported ease of use. The less complex phone (Nokia) performed significantly better than the complex one (Siemens). However, the benefit from the lower complexity was much larger than theoretically predicted. Thus, defining cognitive complexity of technical devices by the number of production rules does not account for the real difficulties which users experience. Older users had a lower navigation performance than younger users, however their performance matched younger users’ when using mobiles with low complexity. 1. Introduction The distribution of mobile phones represents one of the fastest growing technological fields ever. Already by 1999, 500 million mobile phones were distributed worldwide. In the United States, the number jumped up from a few thousand in 1983, to over 10 million in 1992 and to about 112 million in 2001, with an increasing trend (Curry 2001). In the foreseeable future, mobile communication will affect entire modern societies even more than today, changing social, economic and communicative pathways by the broad insertion of mobile communication technologies, such as the Internet, UMTS (Universal Mobile Telecom- munications System), Wireless LAN and WAP (Wireless Application Protocol) services. The variety of functions capable of running on these small devices with small sized displays is enormous. However, it is rather difficult to implement the complexity of functions in such a way that the devices provide good usability and, consequently, allow universal accessibility. According to Dix et al. (1998), usability is conceived as the ease with which users interact with the device, achieving optimal performance with respect to effective- ness, efficiency and users’ satisfaction (EN ISO 9241- 11 1997). The claim includes the phone to be designed so that users’ knowledge and experience in related areas can be adopted when confronted with an unknown device. As can be observed rather often though, the usage of modern technical devices is not conceived to be easy, but to impose considerable cognitive load on users. What makes the handling of hierarchically built technical systems – for example the cell phone – so difficult? A fundamental component leading to problems in its usage is the restriction of information access due to the small sized display. Only a few items can be seen at a time and users navigate through a menu whose complexity, extension and spatial structure is not transparent to them as it is hidden from sight. As users have to memorize the functions’ names and their relative location within the menu and build a mental map of the menu structure for a proper orientation, they may experience the feeling of having little control over the phone, often not knowing what to do next, when to do it and how to complete a targeted action successfully. Recent studies substantiated the usability of mobile phones to be of central ergonomic concern, not only for *Corresponding author. Email: Martina.Ziefle@psych.rwth-aachen.de Behaviour & Information Technology, Vol. 24, No. 5, September 2005, 375 – 389 Behaviour & Information Technology ISSN 0144-929X print/ISSN 1362-3001 online # 2005 Taylor & Francis http://www.tandf.co.uk/journals DOI: 10.1080/0144929042000320009