• by Jack Loechner , Staff Writer @mp_research, January 23, 2009

According to a new study by Epsilon on the importance of the subject line in an Email promotion, shorter subject lines do generally perform better than longer ones, but the relationship between subject line length and response is weaker than previously thought. Though the research showed that, overall, shorter subject lines correlate with higher open rates and click rates, subject line word order, word choice, and brand and audience awareness are also critical success factors.

A subject line is often the first opportunity an email marketer has to capture a consumer's attention, says Epsilon. Multiple analyses have shown that the subject line is the most important factor in driving overall response, from initial Epsilon clients the subject line is almost always the factor most responsible for open and click to eventual conversion. In more than 20 multivariate tests with 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.

Thane Stallings, Senior Analytic Consultant, Epsilon Strategic Services, says that "Companies are spending little time thinking about and testing subject lines, compared to the resources and time devoted to creative development. The reality is that more people will see a subject line than its accompanying creative."

However, the superiority of shorter subject lines (SLL) isn't solely a function of consumers' busy lives and short attention spans, says the report. In fact, SLL is often predetermined by technical constraints.

The Epsilon Whitepaper reports that Email 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 a 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

Therefore, 57% of U.S. email recipients see only the first 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.

The report says that, 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. Epsilon calls this technique "pole position" writing. For one email campaign, the vital piece of information may be the brand name. For another, it may be the consumer benefit. Only systemized testing can reveal what works best in each situation and for each consumer population.

From an analysis of the impact of the more than one billion emails over nearly 20,000 separate campaigns sent out by a selection of US-based clients in the retail and consumer services industries, Epsilon concludes that because higher open and click rates depend on the optimum combination of SLL (subject line length) and content, marketers should keep in mind the following rules of thumb:

• Front load subject lines with the most important information
• Keep the subject line as short as possible to convey the message
• Use longer subject lines only when there is a compelling reason to do so
• When in doubt, test

Correlation Between SLL And Response For CONSUMER SERVICES COMPANIES
	Avg. Open	Avg. Click	Avg. SLL	Open/ SLL Correlation	Click/SLL Correlation
Client 1	14.0%	3.8%	37.8	-0.42	-0.59
Client 2	21.5%	2.0%	47.8	0.04	-0.04
Client 3	33.0%	12.6%	36.4	-0.15	-0.03
Client 4	33.8%	12.0%	36.2	-0.15	0.04
Client 5	15.6%	3.3%	48.0	-0.46	-0.23
Average			41.2	-0.23	-0.1 7
Source: Epsilon Whitepaper, January 2009

 

Correlation Between SLL And Response For RETAIL COMPANIES
	Avg. Open	Avg. Click	Avg. SLL	Open/SLL Correlation	Click/SLL Correlation
Client 1	33.9%	7.3%	39.1	0.06	-0.21
Client 2	37.1%	9.8%	44.2	-0.02	0.09
Client 3	28.6%	8.1%	37.8	-0.15	-0.28
Client 4	42.1%	21.5%	29.7	-0.31	-0.09
Client 5	19.2%	6.5%	30.8	-0.08	-0.19
Average			36.3	-0.10	-0.1 3
Source: Epsilon Whitepaper, January 2009

Epsilon concludes that this new research confirms the widely held belief that, in most cases, shorter subject lines perform better. However, the research suggests that the way in which content and brand messaging are positioned can be as important to email success as the number of characters in the subject line. While a host of studies show that shorter subject lines improve email performance, Epsilon's research indicates that the relationship between SLL and performance is weaker than is widely believed. Other marketers have found that with specialized audiences, longer subject lines often deliver higher open and click rates. But in all cases, subject line content continues to be a vitally important element in delivering response.

Please explore the findings in greater detail at Epsilon.com here, or read the complete Whitepaper here.