**8. Usability, accessibility, and acceptability of diabetes apps**

In a study of feasibility and acceptability of PDA-based (personal digital assistant-based) dietary self-monitoring of diabetes patients at the time of advent of the first smartphone high percentage of participants reported that they found PDA-monitoring useful, that the app was easy to use and that feedback was easily understandable [107]. In another study with PDAs, several limitations were found that may have contributed to perceived frustration including usability, data loss/errors (especially mistyped numbers) and time constraint (time consuming and tedious handling) [108]. A new study revealed that the perceived additional benefit and the perceived ease of use had the strongest impact on acceptance of diabetes smartphone technology by patients 50 or older. Less important factors were previous experiences, health status, support, confidence in own technical knowledge, perceived data security, and fault tolerance. The target group of diabetes patients aged 50 or older is a rather heterogeneous one and their needs are highly heterogeneous due to differences in previous knowledge, age, type of diabetes, and therapy. For that reason, it is impossible to address the needs of all diabetes patients adequately with one diabetes app in order to gain an additional benefit. Therefore, the contents of a helpful diabetes app should be individually adaptable [109]. There is a lack of systems that can perform automated translation of behavioral data into specific actionable suggestions that promote healthier lifestyle without any human involvement. The first attempts were made to create personalized, contextualized, actionable suggestions automati‐ cally from self-tracked information [110].

Ten percent of all available apps in 2013 were evaluated within usability evaluation by three experts considering the special requirements of diabetes patients age 50 years or older. Four main criteria were evaluated, being "comprehensibility," "presentation," "usability," and "general characteristics." The main criteria, "comprehensibility," rated best. In particular, the elderly benefit from easy, understandable semantics and easy, comprehensible, and interpret‐ able images and depictions. It can lower inhibition thresholds, especially during the first time of use. The same is true for the influence of "easily understandable feedback" and an "intuitive usability" (main criterion "usability"). However, these two subcriteria performed worse within evaluation. Test of accessibility features indicated a very good operability of the screen readers. The criterion "fault tolerance" rated worst. Especially, inexperienced (elderly) users often have difficulties with inputting data. Some errors are unrecoverable or even cause the application to shut down [58].
