The topic of email subject lines always generates interest (and some debate) as marketers try to fight through inbox clutter that sees consumers receiving a reported average of 416 commercial emails per month (and that was 2 years ago). A couple of recently-released studies provide some fresh data to review.
(Requisite disclaimer: the following results will not necessarily apply to all readers, who are encouraged to test their subject lines.)
First, a look at a study from Return Path [pdf], based on an analysis of “9 million subject lines received by more than 2 million subscribers from January 1st through February 28th, 2015 using its Subject Line Optimizer solution.”
Right off the top, an interesting finding: the analysis finds no correlation between subject line length and read rate. That stands in apparent contrast to research from MailerMailer last year, which had linked shorter subject lines to higher open and click rates (though significance was not tested).
In the Return Path study, subject lines with 61-70 characters had the highest read rate, of 17%, almost twice the read rate of subject lines with more than 100 characters. Both were not heavily represented, though, comprising just 6% and 3% of messages analyzed, respectively. The most commonly used length was 41-50 characters, in one-quarter of emails analyzed.
The researchers caution that just because there isn’t a relationship between subject line length and read rate doesn’t mean that marketers should not pay attention to length. That’s because different devices will display subject lines in different ways, with desktops typically showing about 60 characters and mobile devices 25-30. As such, the authors remind that it’s more important to place a CTA at the beginning of a subject line if the audience is primarily mobile.
Turning to the performance of various keywords, the following list highlights some of the terms associated with the highest and lowest read rates:
Meanwhile, in a separate study [download page], Phrasee takes on email subject line analysis via a look at 700 million emails in the retail and e-commerce sector, primarily from the US and the UK. The analysis generated a “Phrasee Score” for each term, with higher scores indicating more reliably positive results from a term or phrase.
Here are some quick takeaways (remember these are limited to retail and e-commerce emails):
Finally, to add to the personalization body of research, the phrase “just for you” generates a higher Phrasee Score than the inclusion of the first name in the subject line.
For more on email tactics, see MarketingCharts’ report, Why Consumers Open Brand Emails.
About the Data: Phrasee describes its methodology as follows:
“This analysis is derived from anonymised response metrics that email marketers have inputted into Phrasee. It’s based on roughly 700 million emails, all in the retail and ecommerce sectors, primarily from the USA and the UK, with a few Canucks, Ozzies and Kiwis thrown in for good measure. It is all very recent data from the last 2 months.
We then took the individual phrases and ran millions of Markov Chain Monte Carlo simulations. This allowed us to create millions more potential outcomes that expanded the data set much further beyond the original 700 million. We time-weighted the training data and built random variance into the model to control for experimental bias. This method is much stronger than purely looking at past results: it allows us to create a predictive model for subject line success… and thus the Phrasee Score.”
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