I just read an interesting post on how clickthrough rates for display ads seem to have stop falling and have levelled out to 0.09%

Now, besides the fact that 0.09% is high or low or whatever you may think it is, there is one passage which I’m not sure I understand.

Just 20.4% of conversions came after clicking on a banner ad. Instead, the vast majority happened among web users who had seen the ad but not clicked on it, and who converted at a later date.

How do you track conversions for people who hasn’t clicked on your ad? Via a smart cookie that is aware of the ad displayed while you were on that page? I’m guessing, I’m not a cookie expert, nor I work for a company which offers online advertising solutions of this kind.

However, aren’t there other possible reasons for that person to end up buying (or, in general, “converting”) than the ad? I don’t know, this statistic feels a bit far fetched, but maybe it’s just because I don’t fully understand how they measure it.

Any idea?