[hinkley]

Rate of traffic on the checkout page, divided by overall traffic.

We see a lot of ghosts in A/B testing because we are loosey goosey about our denominators. Mathematicians apparently hate it when we do that.

[plagiarist]

That doesn't test noticing the button, that tests clicking the button. If the color changes it is possible that fewer people notice it but are more likely to click in a way that increases total traffic. Or more people notice it but are less likely to click in a way that reduces traffic.