People with experience in black box trading are welcome to answer this question too.
The problem is as follows: keywords are purchased on advertising network (pay-per-click search engines such as Google), a bid is placed every day for each keyword, and revenue is generated when the click converts (e.g. when the user subscribe to a newsletter).
Each day, we know how much money is made, per traffic segment. The question is: what important metrics should be used to assess the quality of a bidding campaign? Of course total profit is very important, but not the only metric. For instance, if positive days generate a $1000 gain and negative days a $950 loss (profit = $1000 - $950 = $50), it's worse than if the numbers were $80 gain, $45 loss and $35 profit. So the ratio gain/loss is critical. How is this ratio called? What other ratios should be considered?