the less you have the better... unless you can find someone who has run extensive tests with the amount of white space on a page vs number of visitors sent to the site and retention (bounce rate). it just makes sense that you would want to "sell" your customer in the top fold - be it a product, idea, or information ... best of luck to you.
I have no stats but have fairly extensive graphic design and desktop publishing experience. I can tell you that insufficient white space makes your publication - whether a magazine, a newsletter, a blog, a website, etc., will make your publication look cluttered and unappealing and will fail to draw the reader's attention to where you want it.
With that in mind, I do encourage you to use that principle as a guide. You can rely on it. It's one of the first lessons of layout.
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