In the world of PPC marketing, the concept of a CPA (Cost Per Acquisition)  is rattled around a lot. Your cost per acquisition is very important when budgeting out your keyword advertising cost, manage your bids, and know when your account is providing you with a profit. However, setting a blanket CPA across your PPC account is not a statistically efficient way to manage your keywords. Behind every keyword is someone that has a unique intent and purpose, and therefore converts at a different rate, and cost. By managing all of your keyword bids based on one CPA across an entire account, you can drive up costs and lower conversion rates. What will end up happening are your keywords that convert at a lower cost, usually brand keywords, you would end up increasing those keyword bids. The keywords that convert at a higher cost, you will end up decreasing bids, or even pausing them all together, causing you to lose out on conversions.

Every keyword converts at a different cost, and therefore must be managed independently, and therefore harkens back to the age old PPC stalwart of organizing your keywords into a theme related hierarchy.  Manage your CPA by campaigns, or even ad groups. Remember that every keyword is unique and cannot be expected to perform uniformly across an entire account.