One way in which we achieve this is by making continued tweaks and innovations to the user behavior and appearance of our ads. In the past, these experiments have included changes to the font styling, coloring, spacing, and other aesthetic components. More specifically, changes such as redesigned ad units and arrows to show additional ads have stemmed from these tests. The purpose of these tests is to identify changes to our product that can bring long-term benefits to our publishers, your site's visitors, and advertisers.
Before rolling out a change to our ads, we test performance for a limited number of ad impressions, which may not apply to all publishers. Although we don't notify publishers of these specific changes in order to prevent bias, we closely monitor the performance of these tests. We also welcome feedback from publishers, users, and advertisers, so feel free to drop us an email.
Link - from Inside AdSense
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