On my AdSense scoreboard, I am getting a one star rating for my multi-screen. however, I am getting five stars for the other categories. My site is validated and compatible for all platforms. What drives the multi-screen rating?
Your multi-screen rating is based on the number of pages that are optimized for multiple screen sizes. i.e. If a number of your pages are not optimized for mobile/tablet viewers, your performance rating will suffer as a result.
To increase this score:
Something else that is worth taking into account:
The multiscreen score is driven by the visual performance of your pages with ads and how they are displayed to mobile and desktop users. The multiscreen score factors all page-views across your account, but looking at a page-by-page analysis, you can improve your overall score.
The best tool for evaluating how to improve this is Google's own Page speed tool.
Check out the User Experience Tab under both desktop and mobile and get optimizing! Cheers!