What does open rate tell you

There has been an lot written about open rates in the past, but there are two posts that stand out to me. One was the EEC’s post on renaming open rate to render rate and Mark Brownlow’s excellent post on what open rate does and does not measure. I’ve also weighed in on the subject. The issue is still very confused.
If asked, most people will tell you that open rate is the number of emails that were opened by the recipient. The problem is that this isn’t actually true. Open rate is measured by the number of people that display an image in an email. Traditionally this has been a uniquely tagged 1×1 pixel, until some filters and mail clients stopped displaying 1×1 pixels. More recently, every image in an email is tagged, so opening one image would record as an open.
So open rate doesn’t actually tell a sender how many people opened and read an email. It really only records that an image in a particular email is loaded. It does not record when an email is opened. Some people don’t load images by default. Some people don’t load images at all, even when they open and actively read the text portion of the email.
Clearly, there are some uses for open rates. It can give a useful metric when comparing different forms of the same email (A/B testing) and when looking at user engagement over time. However, we have also recently seen that open rate is not predictive for click through rate.

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When an open is not a sign of interest

A lot of people, including myself, are using opens as one of the measures of engagement. This, as a general rule, is not a bad measure. However, there are people who will open email not because they’re interested in it, but because they know it is spam.
Take, for instance, the email address I acquired in 1993. Yes, I still have this address. I stopped using it to sign up for lists in 1999 and stopped using it for most of the rest of my mail around 2001. This address, though, is on any number of spam mailing lists. The spam that gets through is usually sent by hard-core spammers. The ISP that hosts that mailbox uses Communigate Pro to filter mail, so much of the casual spam is filtered.
Generally, if I open an email (and load images or click through) on that account it is only in order to track down a spammer. For instance, I’m getting a lot of spam there from affiliates offering me the opportunity to purchase printing services for a very low price. I have actually been opening the mail, and clicking through. But I’m not clicking through because I’m interested in purchasing. I’m clicking through to see if my reports to abuse@ printer are resulting in any action against the spammers. (They’re not).
The thing is, though, I know that by clicking through on ads, I’ve now been promoted by the spammer to the “clicks on emails! it’s a live address!” list. Which only means I’m going to get more spam from them. Lucky me.
Using clicks and opens as a measure of engagement isn’t necessarily bad. But when using them you have to understand the limitations of the measurement and that what you may think it’s telling you isn’t actually what it’s telling you.

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Measuring open rate

In this part of my series on Campaign Stats and Measurements I will be examining open rates, how they are used, where they fail and how the can be effectively used.
There has been an lot written about open rates recently, but there are two posts that stand out to me. One was the EEC’s post on renaming open rate to render rate and Mark Brownlow’s excellent post on what open rate does and does not measure. I’ve also weighed in on the subject.
Overall, I find open rates to be a very frustrating metric. Some senders, particularly those relatively new to email marketing, are so sure they know what open rate is and what it means, that they don’t take any time to actually understand the number. While the name “open rate” seems self explanatory, it’s actually not. Open rate is actually not a measure of how many recipients open an email. However, there are times where open rate is a useful metric for measuring a marketing program over time.
What is an open?
If asked, most people will tell you that open rate is the number of emails that were opened by the recipients. The problem is that this isn’t actually true. An open is counted when a tagged image in an email is rendered by the recipient’s email client. Not all mail clients render images by default, but the emails are still available for the recipient to read. If a user clicks on a link in an email that has not had an image rendered, some ESPs count that as an open as well as a click. In other cases, visiting a link in an email with no image rendered is just a click, no open is recorded.
What is the open rate?
Open rate is generally the percentage of email opens divided by some number representing the number of emails sent. Many senders use the number of emails sent minus the number of bounced emails, others use just the number of emails sent without factoring in the number of emails bounced.
Open rate is a secondary metric. While it does not measure the success, or failure, of a campaign directly, it can be used as a indicator for campaigns. Many people use open rate as a metric because it’s easy to measure. Direct metrics, such as clicks or average purchase or total purchase, may take days or even weeks to collect and analyze. Open rates can be calculated quickly and easily.
What the open rate isn’t
Open rate is not a measure of how many people opened a mail. It is not a measure of how many people read a mail. It really only records that an image in a particular email is loaded and, sometimes, that a link was clicked on. Open rates can be wildly different depending on how the sender measures opens and how the sender measures sends.
What senders use open rates for
To compare their open rates with industry averages
As I talked about above, this use of open rates is problematic at best. You cannot compare numbers, even when they have the same name, if the numbers were arrived at using different calculations. Open rate is not open rate and unless you know the underlying algorithm used you cannot compare two open rates. This is a poor use of open rate.
As a metric for advertising rates
Since a sender can manipulate the open rate by using different calculation methods, this is a good metric for the advertiser to use. It is not so great for the purchaser though, who is at the mercy of the sender’s metrics. There are contractual ways a purchaser can protect herself from an unscrupulous marketer, but only if she understands how open rate can be manipulated and takes steps to define what open rate is in use.
To judge the success of campaigns over time
A single open data point doesn’t mean very much, however, using consistently measured open rates a sender can measure trends. Open trends over time are one area that open rates can help senders judge the success, or failure, of a marketing campaign.
As one metric in A/B testing
Comparing open rates in A/B testing gives some indication of which campaigns recipients may be more interested in. As with trends over time, the lone measurement isn’t useful, but as a comparative metric, it may provide senders with insight into a particular mailing.
To judge the engagement of recipients
Over the long term, recipients who do not interact with a mailing become dead weight on the list. Too many non responders can hurt a sender’s reputation at an ISP. List hygiene, in the form of removing people who never open or click on an email, is an important part of reputation management.
As metrics for email campaigns go, open rate is limited in what it measures about an email campaign. However, as a quick way to measure trending or do head to head comparisons it is a useful metric.

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Delivery Metrics

Last week ReturnPath published a study that shows 20% of permission based email fails to be delivered to the inbox. For this study, ReturnPath looked at the mail sent by their mailbox monitor customers and counted the number of deliveries to the inbox, the number of deliveries to the bulk folder and the number of emails that were not delivered.
At US ISPs 21% of the permission based emails sent to the ReturnPath probe network did not make it to the inbox. 3% of the emails sent went to the bulk folder and 17% did not make it to the mailbox at all.  MSN/Hotmail and Gmail were the worst ISPs to get mail to. They each failed to deliver more than 20% of the mail that was sent to them. At Canadian ISPs, even less of the mail made it to the inbox, primarily because primus.ca is such a large portion of the Canadian market and they use Postini as a filter. Postini is a quite aggressive filter and takes no feedback from senders.
ReturnPath’s take home message on the survey is that one set of metrics is not enough to effectively evaluate a marketing program. Senders need to know more about their mailings than they can discover from just the bounce rate or the revenue rate or response rate or open rate.
There are a lot of reasons an email doesn’t get to the recipient’s inbox or bulk folder. Mail can be hard blocked at the MTA, and rejected by the ISP outright. Mail can be soft blocked at the MTA and the ISP can slow down sending. Sometimes this is enough to cause the sending MTA to stop attempting to deliver the mail, thus causing mail to not show up. Both of these types of blocks are usually visible when looking at the bounce rate.
Some ISPs accept mail but then fail to deliver it to the recipient. Everything on the sender end says the ISP accepted it for delivery but the ISP just drops it on the floor. This is the type of block that a mailbox monitoring program is best able to identify.
Despite all the discussions of numbers, many marketers are still not measuring the variables in their email campaigns. Ken Magill wrote today about a study released by eROI that indicates more than a third of marketers are not doing any testing on their mailings.
Now, both of these studies are done in an attempt to sell products, however, the numbers discussed should be making smart senders think about what they are measuring in regards to their email campaign, how they are measuring those factors and what the measurements mean.

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