Strength of Evidence:
Document Type: Guideline
Text and Styles
When users must read a lot of information, use lower-case fonts and appropriate capitalization to ensure the fastest possible reading speed.
Using 'mixed-case' fonts for reading prose text means that most letters will be lowercase, with all letters that should be capitalized being in uppercase. Most users have had considerable experience reading lowercase letters and are therefore very proficient at it.
Related Usability Guidelines: