<i>&gt; I&#x27;ve personally run tests and seen tests achieve statistically significant (and very large) results that weren&#x27;t merely fixing bugs or moving buttons within reach of a user. It could be things like adding a modal, changing copy (yes, literally just adding or changing words on the page), removing content, changing an image, or reordering funnel steps.</i><p>You should read the article. It explained very well why a) statistical significance is meaningless when split testing websites (you are guaranteed to archive significance if you run the test long enough; the math behind significance testing doesn&#x27;t work like assumed by Optimizely et.al.) and b) most tools on the market are inherently unable to prove effect size by the way tests are designed.<p>Just do this short experiment yourself: Do an a&#x2F;b test with <i>identical</i> versions of you site. Spoiler: With 100% certainty, you&#x27;ll see both significant results <i>and</i> a sizable effect size difference.