“Negative” metrics — You might prefer the term “Deoptimization Metrics”. Either way they can be just as important to your continuous optimization efforts as your positive ones. The purpose of a negative metric is to isolate for you the deleterious effect you may be having on your positive metric.
A negative metric is not necessarily something you want to get less of — for example, “reduce bounce rate”. That’s just an easier way to state the positive inverse of “increasing the un-bounce rate”. Rather, a negative metric is something you look at to ensure that when you have success with your positive metric, you aren’t penalizing yourself somewhere else. I covered this when I discussed the value of nothing earlier.
Read this entire article over at my MarketingLand.com column
I do have an article post on setting up negative metrics for your tests, along with an example from a completely different direction.