An Uplift refers to an observed change for a given metric between a variation and the control. A 0% uplift means ther’s no difference between the variation and the control, and a negative uplift (or downlift) means that the control actually did better than a variation. We express this change as a percentage. For example, if the control has a Conversion Rate (CR) of 4%, and the variation has a CR of 5%, we say this is a 25% percent uplift, since 5 is 125% of 4.