A subject line is often the first opportunity an email marketer has to capture a consumer’s attention. Multiple analyses conducted by Epsilon have shown that the subject line is the most important factor in driving overall response, from initial open and click to eventual conversion. In more than 20 multivariate tests with Epsilon clients — using statistical methods to systematically vary creative content, placement and design to establish the winning combination, or “super email” — the subject line is almost always the factor most responsible for triggering opens and clicks. Common sense also underscores the vital importance of the subject line; it is one of the few factors consumers consider when deciding whether to open an email.
Despite the widely acknowledged importance of subject lines, companies often don’t test their effectiveness. They spend little time thinking about and testing subject lines, compared to the time and resources devoted to creative development, even though significantly more people will see a subject line than its accompanying creative.
Much has been written on one particular aspect of subject lines: the length. Most research on this topic concludes that shorter subject lines are better.
Other studies claim that longer subject lines work best. New research conducted by Epsilon confirms that shorter subject lines generally outperform longer ones but also quantifies the relationship between subject line lengths (SLL) and open and click rates. Additionally, the Epsilon findings discussed here suggest that word order and selection are vitally important considerations in subject line effectiveness.
This white paper reviews new research on the relationship between SLL and response, and proposes a framework for evaluating SLL as it relates to email marketing efforts.
Why is SLL Important?
In its 2007 Email Benchmark Guide, Marketing Sherpa concludes, “When it comes to subject lines, shorter is better. It’s as close to a universal rule of the
Internet that simple messages that can be instantly digested are the best way to take advantage of our short digital attention span.” However, the superiority of shorter subject lines isn’t solely a function of consumers’ busy lives and short attention spans. In fact, SLL is often predetermined by technical constraints.
Always remember that Email Service provider domains often limit the number of subject line characters displayed by default in the inbox.
AOL, which is responsible for approximately 22% of the U.S. email market, limits subject lines to roughly 38 characters.
Yahoo!, with 21% of U.S. email, has an approximate limit of 47 characters per subject line.
Hotmail, which has 14% of the U.S. email market, uses word wrap to display subject lines on multiple lines, allowing approximately 45 characters per line.
If you’re aware that a substantial number of your supporters may be reading your emails on a mobile device, consider condensing your subject lines even shorter. Some mobile devices (iPhone, for example) can show most of the characters in a subject line, while others (such as the BlackBerry) tend to show fewer than 10. In these cases the “from” line may be more important for getting recipients to open your email.
Therefore, 57% of U.S. email recipients see only the fi rst 38 to 47 characters of a subject line when making the decision to open an email. Additionally, the growing reliance on mobile devices — and their smaller screens that display even fewer characters —affects this trend as well.
Subject Lines: Beyond Length
Consider the following subject line couplet:
Subject line 1:
“This weekend only at your local Acme Store, special savings on Ladies Apparel!”
Subject line 2:
“Special savings on Ladies Apparel at your local Acme Store this weekend only!”
These two fictitious subject lines are identical in length but differ greatly from a functional perspective.
The first subject line follows a time>brand>benefit > category structure.
The second follows a benefit>category>brand>time structure.
In all likelihood, these two subject lines would not perform the same. But without knowing the brand and the audience, a marketer would be challenged to predict which would perform better. This scenario illustrates how word order and word choice can trump absolute length.
Another example:
Subject line 1:
“Last chance to order for Valentine’s Day is this Wednesday, Order Now”
Subject line 2:
“Only 48 hours to order for guaranteed Valentines Day delivery”
Subject line 2 is shorter and uses a numeral in the subject line (a widely accepted best practice), yet subject line 1 provided a 23% lift in sales for the florist that sent it. Why? It may be due to the absolute deadline (“this Wednesday”) versus the relative deadline (“only 48 hours”) in the second subject line.
Also, subject line 2 adopts the point of view of the company (48 hours from when message was sent, not 48 hours from when the subject line was opened), versus the point of view of the recipient. Thus, the first subject line may have been less confusing to the consumer. Finally, the fi rst subject line referred to the holiday earlier in the subject line than the second subject line and used the ultimatum “last chance.” This example highlights two points: first, subject lines can have an enormous impact on a company’s bottom line, not just their open rate; second, subject line testing is difficult.
A final example:
Subject line 1:
“U.S. May Face Shortage of General Surgeons”
Subject line 2:
“4/29/2008: U.S. May Face Shortage of General Surgeons”
The only difference between these two subject lines is the date at the beginning of subject line 2. In this case, subject line 2 performed slightly better in terms of opens and clicks. Simply put, sometimes a longer subject line is justifi ed by an element that increases response. Other examples of this phenomenon are the inclusion of brand messaging or personalization in the subject line.
Exceptions to the Rule
According to MailChimp, an email service provider specializing in smaller clients, “The general rule of thumb in email marketing is to keep your subject line to 50 characters or less.... The exception was for highly targeted audiences where the reader apparently appreciated the additional information in the subject line.” One email program that qualifi es as MailChimp’s exception to the rule is the Kimberly-Clark brand GoodNites®, which markets products for children with bedwetting challenges.10 Over the past year, GoodNites has averaged a whopping 94 characters for its subject lines—2 to 3 times longer what is commonly accepted as a “best practice.” Longer subject lines simply perform better for the brand, with SLL correlating to a unique open rate and total click-through rate of .47 and .53, respectively—high correlations by marketing standards. In fact, in 14 of 22 (64%) recent A/B or A/B/C subject line
tests, the longer subject line performed better, regardless of subject line content.
One tactic that GoodNites employs in its subject lines is the use of lists, as in the example: “4 Bedwetting Causes, Parents Helping Parents, Valuable Coupon and More!” In GoodNites’ case, the extra information afforded by the longer subject line helps GoodNites reach a wide variety of consumers who are at various points in their relationship with the brand.
Ellen Watson, the member of Kimberly-Clark’s Media and Relationship Marketing team who manages the newsletter, says, “Someone who is just starting to confront the issue of bedwetting might be searching for advice and information, whereas someone loyal to the product would be more interested in coupons or special offers, and a highly engaged member of our online community might be interested in hearing stories from other parents. Our longer subject lines can speak to all these consumers at once.” Also, GoodNites’ extensive use of compound subject lines with short, pithy statements allows the subject line to be digested at multiple intervals, independent of the subject line’s appearance in the Consumer’s inbox.
In terms of domain limitations, an AOL consumer might see the GoodNites subject line as “4 Bedwetting Causes, Parents Helping P,” whereas a Yahoo! consumer would see “4 Bedwetting Causes, Parents Helping Parents, Valu.” Although the subject line would be incomplete in both inboxes, it still holds meaning. For even higher response potential, GoodNites should test the order of subject line elements, given that not all elements will be visible from the inbox. Given that most U.S. consumers see only the first 40 characters or so of a subject line, marketers should be careful to construct the subject line in such a way as to include the most vital information first.
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