“Inferred CTR” method for reducing cannibalisation of SEO
How PPC cannibalises your SEO traffic
A lot of the time your PPC campaigns may be cannibalising your own SEO traffic. In other words, some of your PPC campaigns are stealing from your SEO. And with often limited marketing budget, you surely would want to make sure that you are spending in the most efficient and incremental way, with little or no negative impact on SEO.
The degree of cannibalisation will depend on three main factors listed below, and should be considered at an individual keyword level.
your SEO CTR (ie Organic CTR)
PPC competition
device (PPC incrementality is expected to be higher on Mobile devices, and much lower on Desktop devices)
SEO CTR
The higher your SEO CTR, the bigger the chance of your PPC cannibalising your SEO traffic. In other words, PPC would be less incremental. For many companies, PPC brand campaigns tend to show low incrementality, and that is simply because for brand terms companies are likely to already have good SEO rankings & CTR (plus potentially also much less PPC competition).
So an easy way to to minimise cannibalisation is to avoid spending PPC budget on keywords with strong SEO CTR (especially if you are ranking already at position 1 or 2). You should instead be spending most of your PPC budget on keywords with poor SEO CTR as these are likely to be much more incremental.
SEO Rankings & CTR data
All of the data required to measure your Organic rankings & CTR at a keyword level can be easily extracted from Google Search Console (so make sure you have it set up for your website). If you do not want to use the Google Search Console interface (which indeed is not very user-friendly), it is probably best to access the Google Search Console data via one of the following (free) ways:
Search Analytics for Sheets (Google Sheet add-on, completely free)
Google Data Studio
Google Search Console API (using R or Python)
PPC Competition
PPC competition is another important factor when it comes to PPC Incrementality. With highly saturated PPC, it might still be worth protecting your share of the traffic with Paid Search, even if your SEO rankings & CTR are strong. The bigger the PPC competition, the less your strong Organic rankings matter, and so your PPC campaigns will be more incremental. In such situation, instead of taking away traffic from your own SEO, you would be taking away traffic from your competitors. Where PPC Competition is low, the Incrementality of your PPC is expected to be lower.
PPC Competition data
Getting PPC Competition data is not as straightforward as it is with your own SEO data. There are however some possible solutions
Google Ads Keyword Planner (that, for each keyword can tell if you the competition is Low, Medium, or High)
Google Sheet tracker (with a bit of skill you should be able to setup a tracker yourself, alternatively Hire an expert to set it up for you; although this solution might be at first more difficult to setup, it actually is going to give you much more accurate and insightful data than the Keyword Planner would)
Device
Generally speaking, incrementality of PPC is lower on Desktop than it is on Mobile. This is simply due to the screen size difference between the two. It takes much more effort for a user to scroll down to the Organic results when browsing the web on a Mobile device. Browsing however on Desktop means a user will see both Paid and Organic results without much of scrolling. For that reason bidding on Mobile is expected to be much more incremental to your business, as even if your Organic position is already very strong, on Mobile it wont really matter that much (unless there is absolutely zero Paid Ads by other competitors).
Example
Below you can see a very simplistic example, and in reality it does not actually have to be anything more complicated than this. Simply start from gathering information about your current SEO CTR by keyword, and rank it from 1 to 3 (with 1 representing high CTR, and 3 representing low CTR). Then also gather for same keyword information about PPC competition, and also rank it (with 1 representing low competition, and 3 representing high competition). Optionally you might want to also include a third factor, that is share of Mobile traffic by keyword (you can take this for example from your Google Search Console Impressions data). Once you gather all (2 or 3) factors, calculate an average of all, and you end up with an Inferred PPC Incrementality score. The higher the score, the bigger the chance that spending your PPC budget on a particular keyword would be incremental to the business. Avoid spending on keywords with low Incrementality score, as you are likely to get most of this traffic for free anyway via your Organic results.
Using just 3 levels is naturally the most simplistic approach, but feel free to be more granular (and use for example 1 to 10 levels, as long as you are consistent across all factors)
