Now that is genuinely interesting. Of course, the raw data is hidden behind a paywall, so we don't really know that "significant" means to the author, or whethe

Now that is genuinely interesting. Of course, the raw data is hidden behind a paywall, so we don't really know that "significant" means to the author, or whether the test included slides or just raw text. Still, this is one of those rare times when I could be right about looking professional (it looks cheesy, can't argue that) but completely wrong if it actually leads to higher retention.