How can the UX of Accessible Services be accurately measured and used to improve the overall experience of using accessible devices?

Digital platforms are used to provide information and services for all members of society. With a reliance on technology comes an increase in the demand for services that are accessible by all. However, accessibility is stereotypically viewed as a bolt-on service and as such a binary approach is taken to creating accessible solutions; services are either accessible or not. It is difficult to identify products that achieve accessibility with the added benefit of being more usable. Accessible services should not be created to be 'good enough' but should make the overall experience of participating in a digital experience seem pleasant to the end user.

We have previously examined UX within accessibility in the development of a framework that focuses on media subtitles and subsequently used this to develop accessible and usable methods of displaying subtitled content on different devices. However, it is unclear what factors should be used to understand the UX of accessible products in general and the importance that these factors have to end users.

In this PhD, we aim to answer the following:
How can the UX of Accessible Services be accurately measured and used
to improve the overall experience of using accessible devices?