EVALUATION OF CURRENT SYSTEM
If a system already exists, a UX professional will holistically evaluate its current state. They will report issues and suggest fixes based on their analysis of research data.
A/B TESTING
A UX specialist might devise a study to compare the effectiveness and quality of experience of different user interfaces.
This is done by stating a hypothesis (e.g. “A green button is more attractive than a red button.”), proposing or creating multiple versions of a design, defining what a “better experience” means (e.g. “The green button is better because users clicked it more.”) and then conducting the test.