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June 12, 2013 / christinazuniga

Investigation: Click Through Rate Decrease

Click Through Rate (CTR) is a valuable statistic to track in your email marketing efforts, it measures the number of clicks against the total number of times the link was viewed. It can tell you how interesting your content is, the preferred email design for your audience and where to locate links to get the best responses. My job is to carefully track this and other statistics, however, I experienced a significant problem with my overall CTR after encouraging my email marketing users to place the same URL in a variety of areas in their emails.

Most email marketing programs and marketing automation systems will provide out of the box reports that calculate the click through rate or supply the raw numbers so that you can calculate it yourself. The equation for click through rate is total number of clicks divided by total number of impressions. Impressions are the number of times a link has been viewed, so click through rate is the number of times a link was clicked out of all of the times that it had the potential to be clicked.


One of the initiatives that I set for my users was to test which link locations are most popular with our contact database. Instead of one link per URL which was the protocol for 2012, I encouraged users to include up to four links per URL placed in strategic areas around their email. This was not intended to be an A/B Test with two groups receiving the same email with links in different places to test their preference for placement or button design; it was meant to add incentive to click the link by adding it in more places.

In 2012 we had a very steady CTR. I cannot share the exact number, but I will give an example number of 5%. After implementing my initiative for 2013, I saw that number plummet in my reports to 2.5%. What had happened that caused my CTR to decrease so dramatically? I had to investigate before sharing the numbers with my users or management.

Some email marketing programs will automatically calculate the click through rate based on the URL given, regardless of the number of times the URL is in the email. This provides an overall click through rate for that URL. My email marketing software provides the click through rate based on the link, which means if the same URL is used in an email three times my software will give me three different click through rates – one for each link despite the fact that it is the same URL for each of those links.

Here’s an illustration of the problem. In 2012 I only had one link per URL and received 10 impressions with 10 links. This means my CTR was 100% – for every view of the email, the link was clicked.


In 2013 I added the same link in two different areas – one in the main body of the email and one in the side bar. Half of my audience clicked one link and half clicked the other link.


However, in calculating CTR, you must get the total click divided by total impressions. So even though I have the same overall clicks (10), I’ve now doubled my impressions (20). This causes my denominator to be much larger, reducing my CRT by half!


Once I had this knowledge, it was easier to fix my data so that my users could continue to add multiple links with the same URL while not reporting an incorrect CTR. I’m happy to say after adding multiple links with the same URL, we’ve seen our CTR increase marginally! It’s important to investigate why your metrics have changed if you see a significant decrease or increase. My calculations could have been an error on my part, over communication with my audience list, or a number of different things. Have you seen sharp changes to your statistics before? It so, why did the numbers change?

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