By comparison, let’s take a look at quality score, which has been repeatedly touted as the most effective way to manage cost-per-conversion.

Using the cost-per-click matched accounts from our previous example, here’s how cost-per-conversion varies with impression-weighted quality score.

At first blush, it looks like a pretty direct correlation—as quality score increases, cost-per-conversion decreases.

In fact, our results are strikingly similar to those reported by Wordstream. Every 1-point increase in quality score reduces cost-per-conversion by 12.84%. Every 1-point decrease in quality score increases cost-per-conversion by 12.84%.