Chronically ill people, especially those with low literacy skills, often have difficulty estimatingportion sizes of liquids to help them stay within their recommended fluid limits. There is aplethora of mobile applications that can help people monitor their nutritional intake butunfortunately these applications require the user to have high literacy and numeracy skills forportion size recording. In this paper, we present two studies in which the low- and the high-fidelityversions of a portion size estimation interface, designed using the cognitive strategies adultsemploy for portion size estimation during diet recall studies, was evaluated by a chronically illpopulation with varying literacy skills. The low fidelity interface was evaluated by ten patientswho were all able to accurately estimate portion sizes of various liquids with the interface.Eighteen participants did an in situ evaluation of the high-fidelity version incorporated in a dietand fluid monitoring mobile application for 6 weeks. Although the accuracy of the estimationcannot be confirmed in the second study but the participants who actively interacted with theinterface showed better health outcomes by the end of the study. Based on these findings, weprovide recommendations for designing the next iteration of an accurate and low literacy-accessible liquid portion size estimation mobile interface.
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