One of the most common questions I get about our SEO A/B testing platform is “why do you measure the results using search traffic instead of rankings?”.
Three main reasons:
Clickthrough rate (CTR) is a huge factor in how much organic traffic you get, and many SEO tests change how your site looks in the search results, and hence affect CTR. No position tracking tool can measure this
Rank tracking can never cover the full tail of key phrases and will miss or misrepresent cases where the effect is different in the head vs in the long tail
Search Console theoretically has CTR data and the long tail, but in practice is sparse, incorrect, or averaged
So organic search traffic is the best proxy for business results - and because sensible tests get more of the same traffic (by ranking better within the same keyword space), we typically see conversions increase with the increase in the organic traffic we are targeting. Essentially Google is doing its job by sending more relevant traffic.
If we’re focused on business results why traffic and not conversions? For the most part, we have found it most powerful to decouple into two different stages - to measure the impact on traffic and on conversion rate separately. Watch this space for more.
Update: since this post was published, we have launched full funnel testing which enables automatic analysis of traffic impact, conversion rate impact and combined net impact.