The answer came to me while reading up on advertising. Studies show it takes a certain frequency – most people place it around 7 times – for an ad and its message to be remembered. It would obviously be silly to just credit the last impression for finally getting the target consumer to get the advertiser’s point when the other 6 clearly were part of the process. Yet that’s a question many pro marketers have!
“Do we credit the first click or the last click for this conversion?”
Answer: You credit them both and the ones in the middle too.
They all played a role. If it turns out your cost-per-action (CPA) is higher than projected now, that’s tough luck – factor it into your measurements and budgeting. You can’t count a single 50 cent click for the conversion when there were 3 other dollars that also made an impact on this new client…
Also, if one or more of those impressions came from the organic side of things, you can either measure the value at PPC cost. E.g. if you’d have to pay a dollar to buy the click, that’s how it factors into the CPA calculation. An alternative is to measure the value of labor/other expenses to rank divided by total traffic pulled on the keyword to get the cost. Obviously this is more complicated, so PPC replacement might be simpler to measure.
This answer to the source attribution question also affects how you structure affiliate commissions and payouts.
Out of the 7 repeat visits prior to purchase, how many did the affiliate send? 1? 2? 4? 7? You don’t want to tick off affiliates, but you need to credit your own inhouse work too. Also, keep in mind some people will purchase on visit 1 and others will purchase on visits 3, 5, 8 or 11. You might need to get more sophisticated with your analytics…
Some other related writing of mine:
View-Thru Attribution Management – answering the Q of giving credit to ads seen but not clicked on.
The Lost Cross Channel Tracking Notes – focused on coupons and tracking online campaigns offline
Attributing Credit When Email And Affiliates Overlap – just what it sounds like
If you like these, add my RSS feed to your reader for more on crediting and web analytics.