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> the very term A/B testing refers to the "A" and "B" sides of a newspaper print roller being able to print two versions of an advertisement.

Really? That's interesting. But how could they tell which version converted better? Maybe distributing each version in a different area?

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That was the beauty of it. As the newsprint passes through, one paper will get A, the next will get B, the next A and so on. The plates are otherwise identical for each page being printed.

This perfect 50/50 split pretty much controls for all the plausible variables. Location, time of day, you name it, the odds of a reader seeing either A or B was exactly 50%.

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