Subject line research has many lessons

Latest posts | Feed | By Mark Brownlow on June 30, 2008

A fascinating study of subject lines by AlchemyWorx (download here) makes critical reading for those interested in optimizing their subject lines (and who isn't?).

Here's the summary:

1. Short subject lines optimize open rates.

2. Long subject lines optimize both clickthrough and click-to-open rates.

3. Subject lines somewhere in between optimize neither the open rate or click to open rates.

In most cases, clicks are more useful to you than "opens," suggesting that longer subject lines are more effective. (But read on: it's not that simple.)

The authors show again the importance of testing assumed truths. In this case, the results challenge the long-held view that shorter is better when it comes to subject lines.

But there's much more to it.

I deliberately do not list the winning subject line lengths (characters and words). Why?

Because there is no magic number of characters or words that is inherently more likely to get someone to open an email or click on a link.

We (me included) have been lulled into thinking of subject lines in terms of length when in actual fact what matters is what you communicate in the subject.

For example, the research discovered that a certain medium subject line length tends to perform badly. Why? Because it often arises when marketers use subject lines which "over simplify or shorten multiple propositions, or unnecessarily lengthen strong, single propositions."

The lesson is not to avoid that medium subject line length, but to avoid the practices outlined in the above quote.

The lesson is not that short subject lines are bad at getting clicks, but that you should use enough subject line to effectively communicate the contents or proposition of the email.

Which, as the white paper authors point out, you might achieve in a short subject line, too.

The big lesson is to get away from a focus on the number of characters in the subject line and instead focus on giving the people who would likely respond to the email's call to action a good reason to take a closer look.

Do this using a compact and concise subject line, but not too compact and concise that this reason isn't adequately communicated. The latter problem is why shorter subject lines performed less well in terms of clicks than longer ones.

And there are more layers of complexity to throw in...

The authors talk about clicks-to-open as a success metric. Be careful here.

Consider a test comparing two subject lines:

Subject line A:
Delivered: 10,000
Opened: 7,000
Unique clicks: 500

Subject line B:
Delivered 10,000
Opened: 3,000
Unique clicks: 300

Subject line B has a higher number of clicks per open, but delivers a whole lot less clicks in total. If you only used the click-to-open rate as a measure of success you'd pick subject line B (and end up with less clicks).

Also, the study looked at opens and clicks because those were the comparative metrics available. For your own emails, you test subject lines using the success measure that makes sense for you: revenue generated, leads generated, downloads, etc.

Then there may be other factors at play. For example, retail emails featuring offers tend to use shorter subject lines than content-based B2B newsletters.

The former often have lower success metrics than the latter. Is it because of the subject line length? Or is it because content-rich B2B newsletters tend to get better numbers than promotional B2C offers?

Do longer subject lines correlate with more success or cause it?

And what happens if you only ever use specific, informative subject lines? Are there long-term brand effects that see people disengage from your emails because they never have to open them to discover the content?

Yes, it is complicated.

All I can say is...read the research, mull it over, and focus on the interpretations given towards the end of the white paper rather than the specific numbers. Then do some tests on your own list and find out what works for your audience and content.

(And keep on challenging those assumptions!)

More on subject lines | Tags: email marketing, subject lines, open rates, clickthrough rates

[This post brought to you by Campaigner Email Marketing]
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