Table 18.

Design Recommendations for common feature component of connected health devices.

Feature	Recommendation	References
Screen Type and Screen Lighting	Low quality LCD screens will often display dull tones and have extremely narrow viewing angles, making it hard for a user to see details on the screen if they are looking at them off centre. This can be avoided by either increasing the screen size or installing higher quality LCD and OLED screens in devices, allowing sharper detail and wider viewing angles.	[21]
Colour	The effects of ageing on colour vision perception may significantly diminish the visual effectiveness of certain colour combinations. Make critical elements larger and ensure that they have high luminance contrast with their surroundings. Warnings should not be solely dependent on colour, but also on visual cues such as flashing, labelling and positioning.	[21]
Character Size	With the advent of touchscreens, adjustable text size will become the norm. Our recommendation is that character size should not go below 12 pt on a High Contrast screen interface.	[21,71,72]
Button Surface Area	Designers should aim for button sizes which allow for easy visibility and easy manipulation. Button surface area should typically reside above 150 mm2	[72,75,78]
Required Button Press Force	-Required push force should not exceed 5 N, and should reside between 2.5 N–5 N. -This is consistent with the AMMI Medical Device Standard, which states that the required press force should not exceed 5 N.	[5,72,75]
Touchscreen	Touchscreen are a more intuitive way of interacting with a display, but poor quality touchscreens are no substitute for good buttons and as such designers should be wary of introducing a touchscreen just for novelty sake. The touchscreen has to be of good quality in order to prevent user frustration and has to have a big enough screen size so as to allow for adequate spacing between elements. It has been shown that older adults can interact effectively with touchscreen interfaces.	[73,74]
Spacing Between Buttons and Touchscreen icons	-For touch sensitive elements of touchscreens, the recommendation is to have pacing between elements of no less than 5 mm with an optimum of 6.35 for older adult users to maintain a frustration free level of accuracy. -Smaller spacing, as little as 1mm, is manageable but will add to user frustration and decrease gadget tolerance. -Spacing between buttons should reside around the same distance as for touch sensitive elements, although by using bigger buttons the need for big spacing decreases.	[74,75,76,78]
Audio Output and Feedback	It is recommended that important auditory feedback reside in the range of 500–1000 Hz with adjustable volume level. When designing tones, beeps and alarms the ATH at each frequency must be taken into account for each age group. It is not just a case of making sounds louder, but also taking into account the frequency at which sounds are transmitted. If including voice feedback on a device via a speaker, the clarity of tone must be optimum otherwise users could easily misinterpret similar sounding words. Similar sounding words should be avoided when possible.	[39,79]
Tactile Feedback	-Tactile bumps and distinguishable surface transitions should be used around important interface elements such as buttons and ports. -Vibration should be used for signalling, especially for seeking attention of the user and as a feedback to show that a button has been pressed correctly.	[40,41,42]
Device Size	-Device dimensions must be such that a user can comfortably hold the device in one hand and still manipulate the controls with the thumb on the same hand.	[52]
Reducing Cognitive Load	-The interface should be based on user-oriented, terms and concepts rather than computer concepts. -The system should display an appropriate level of consistency. Commands and menus should have the same format. -If a command operates in a known way, the user should be able to predict the operation of comparable commands. -The system should provide some resilience to user errors and allow the user to recover from errors. -Some user guidance such as help systems, on-line manuals, etc. should be supplied	[68]