Subject lines: scrabble has the answer

Back in November we had a six-part series on subject lines. But it's already time to reprise the topic in light of some new research.

So shorter is better (or not)? What?

Studies on subject line length tend to put all the emails with a particular length of subject line together and calculate the average response. Then they repeat the process for other subject line lengths. Then they compare the averages to draw out conclusions on the best length.

A problem is that most such studies aggregate numbers across different senders, industries and email marketing models. This can introduce bias and mask more nuanced insights.

Instead of asking whether short is better than long, we should really be asking..."When is short best? When is longer better?"

New research from Epsilon tackles some of these limitations by reviewing data on length and responses (open rates and click rates) for individual companies in single sectors.

The general conclusion: shorter subject lines are correlated with higher responses.

But because the research looks at single companies, it also identifies some of those desirable nuances. Notably:

1. The strength of the association varies from company to company (i.e. length is more critical for some companies than for others.)
2. In some cases, the correlation is reversed (i.e. longer subject lines work better for some companies.)

Thane Stallings, Senior Analytic Consultant at Epsilon, told me:

"The research does show a correlation between subject line length and both open and click rates, albeit a small one. So shorter subject lines do work better, but to say that the length of a subject line is all that's important is to say that short pamphlets make for better literature than long novels."

"The correlation between length and response is small enough, however, to indicate that other factors are at play, but I can only conclusively say that length has a negative impact on response and hint at what I think the other influencers are: word order and word selection."

The Scrabble theory

So what's going on here? Why are some (most) people finding short subject lines work best, while others find the opposite? How can that happen?

As Thane points out, while subject length does matter, other factors can override its impact. Enough to make longer subject lines work better in special circumstances.

Scrabble offers an explanation. In Scrabble, each letter tile has a point score. You put the tiles together in a word and add up all the points for a total. If the word is in the right place on the board, you get a multiplier bonus thrown in, too.

A word or phrase in a subject line has a point score, related to its likely impact on response. So "Free shipping" has a high point score. "Available in different sizes" probably has a lower one.

Putting all the words together gets you a points total for the subject line.

But there are multiplier bonuses to be won. The nearer the word is to the beginning of the subject line, the bigger points bonus it gets.

Why?

Partly because words at the beginning get more attention. And partly because subject lines are truncated in many email clients and webmail interfaces, so the words at the back are more likely to get cut off.

Anyone playing subject line scrabble puts their high scoring words at the beginning. Thane, again:

"I think the realization that most consumers see truncated subject lines is an important one and may explain why shorter subject lines perform better. A marketer who works to keep her subject lines short displays more restraint and discipline."

"If she keeps her subject lines to 45 characters (or so) then there's a 100% chance that all consumers can read the subject line in its entirety from their inbox. But longer subject lines may lack the discipline of having the most important information first: the whole front-loading or 'pole positioning' strategy."

However, our Scrabble theory suggests we should just keep adding point-scoring words, so longer subject lines would always outpoint shorter ones (i.e. get more response).

Now throw in a penalty for each additional word in your subject line. And increase that penalty as the line gets longer.

Now you have a balancing act. Adding a word or phrase to your subject line gets you more points, but also incurs a length penalty.

So you only keep on adding words/phrases until the positive impact is outweighed by the negative.

For most situations, you don't have enough good point-scoring words to justify a long subject line. But in some situations, you do. Which is why shorter is mostly better, but not always.

For a typical, single offer promotional email, once you've mentioned the item, discount and free shipping, nothing much else you can say is likely to boost interest enough to outweigh the subject line length penalty. So shorter works better.

But...if an informational newsletter covers different topics in one issue, each additional topic listed in the subject line engages another group of recipients and boosts response. Perhaps enough to make longer subject lines work better than short ones.

The trick...the skill...the art of subject line writing is knowing which words, phrases, items, topics, questions, branding elements or personalization give you the best response boost.

Only then can you know the right words to use (and how many).

Most important of all, the response value of each word or phrase depends on your email model and your audience (and even on the other words in your subject line - and their order!) Which is why experts place so much emphasis on subject line testing.

Confused? Here's the simpler alternative.

More on email subject lines | Tags: email marketing, subject lines

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