Full disclosure: I work for Qubit who published this white paper. This kind of "historical testing" (I think people often call it sequential testing?) can be p

Full disclosure: I work for Qubit who published this white paper. This kind of "historical testing" (I think people often call it sequential testing?) can be pretty dangerous even for large effects. For example Christmas might be a really good time to change the colour of all the buttons on your site and see a 50% increase in sales.