Using PHP setcookie() for an adsense test

I have wondered for a long time whether people who come to my site via google behave differently in respect to ads than other users. There are lots of reasons for wondering this but specifically for now I am thinking that potentially someone who has just come from google may be more likely to click on an adsense link than someone who has come from somewhere else.

Thankfully I have 10s of k’s of ad impressions daily to test this on and the technology isn’t exactly challenging. I have set up a cookie on every page of my largest site that drops on a users computer once every 72hrs where they have been referred from.

Then lower down the page on every page I have a similar include that powers my advertising. Within this include I read in the cookie and test whether it contains the string “.google.” (not perfect I know but good enough for my purposes.

Note the === in the strpos() function is because strpos() doesn’t always return false when it is false therefore you have to look for responses equivalent to false (===) rather than just equal to false (==). So for me this looks like it could be a really interesting test, I will of course paste the results of the test here and if there’s any substantial difference in results I will of course make changes to capitalize.

I may choose later to also split out people with cookie blocking (since I love vinny’s article) and see how they behave but for now I will just let the results tick over like this for a couple of weeks.