Apparently instead of comparing the number of unique people that clicked an email campaign to the number of email that didn’t bounce (sometime called the number delivered) people are now comparing them to the number of opens. So in the past we did:

unique clicks ÷ (sent – bounced) = CTR

Instead, now people are doing:

unique clicks ÷ unique opens = CTR

If that formula looks familiar to you its probably because its what we used to call the “Click-to-open-ratio” or CTO. I’m curious when this happened.

If you’re wondering why it matters, imagine an email that went to 100 people with no bounces. 10 people opened the email and 1 person clicked. Under the old formula we’d say that this email had a 1% CTR. Under the new formula we get a 10% CTR. If you moved from one email vendor to another and they each used a different formula you’d be seeing a tenfold increase (or decrease) without any of the base numbers actually changing.

So the moral? Make sure you run the numbers yourself so you know what the ratios mean.