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6 things that affect subject line performance

Ah, human language…


Yes. Yes it is.

Take the title of this blog post, for instance.

We could’ve gone with “6 things to consider when writing your next subject line”, or “Subject line performance: 6 things to consider”, or even “6 things that make subject lines better.” The possibilities were endless.

Maybe you like one of those titles better. Perhaps you think one of them would’ve driven more page views.

And you could be right.

But who’s to say?

Well, we’re the ones with the UK Blog award on our shelf, and we have made our choice.

So get off our case.

6 things that affect subject line performance

1) Sentiments

6 things that affect subject line performance

It’s not what you say, it’s how you say it…

As we at Phrasee have said many times; words matter. But when it comes to email subject lines, what matters even more is sentiment. When all the individual words you have chosen to use in your subject line are combined together, they form the message you are sending out to the world, the big question is: what is that message?

How your subject line will be received and interpreted by your audience will determine how effective it is in the end. Is that message on brand? Does it convey the sentiment you hoped it would?

These are all valid questions, and tough ones to answer.

But there is a solution.    

Using our proprietary sentiment analysis tool, you can quantify the core semantic components that exist within any given subject line. Now – and bear this in mind – that semantic constructs (or “emotions” if you prefer) are only one factor in determining how successful a subject line is. They matter – but they’re not the only thing that matters.  

2) Length

6 things affecting subject line performance

Does subject line length matter? No. Well, sort of…

The length of a subject line is actually a proxy of information content. Sometimes the message you want to get across in a subject line will require more words, sometimes it will require fewer. The important thing here is the message, not the number of words you use to convey it.

Trust us, we’ve studied this at great length (pun alert!).

Loads of bad statisticians will tell you that subject line length matters. Well, it does, insofar as it’s a proxy metric. But most say it matters for the wrong reasons (and using bad stats).

To focus on the length of an email subject line is to miss the point.

3) Emojis!

6 things affecting subject line performance

Do emojis work on your audience?

They just might. Many brands have found them to be extremely effective in driving email open and click rates.

Our data tells us that an emoji can make a good subject line better and a bad subject line worse. If your audience responds well to subject lines with emojis in them, use emojis.

The thing to remember with emojis is that they are a visual tool which assists to amplify a message. Just make sure that message is a good message.

4) Phreshness

6 things affecting subject line performance

Your audience is diverse, so your subject lines should be too…

Different words, phrases and sentiments will work on different subscribers on your mailing list. This is why it is important to measure the diversity of the subject lines your brand is using. Keeping as much variation as possible in your subject lines will ensure that they connect with more of your subscribers more regularly, which is a good thing.

In addition, our data shows that the effectiveness of individual words and phrases in an email subject line – its basic elements – decays over time. What works today may not work tomorrow.

Keeping content fresh, diverse and on-point is key.

5) Language sophistication

6 things affecting subject line performance

How sophisticated should your subject line language be?

Are you using complicated sentence structures and polysyllabic words, or simpler language?

Every audience is different, and each will respond positively to slightly different levels of language sophistication.

Try testing subject lines which present your message in simpler language, you might be amazed how your audience responds.

6) Individual word choice

6 things affecting subject line performance

Words matter. Sometimes…

While underlying sentiment is the biggest factor in email subject line success, individual words (and groups of words) can have an impact as well.

Bigrams (word pairings) and trigrams (groups of 3 words) can often provide more benefits to subject line performance than individual words (unigrams) can. Understanding which unigrams, bigrams, and trigrams work on your audience can help your brand build better subject lines, which will drive more opens, clicks, and conversions.  

You can test out all of these things yourself if you choose – but the key is to have a robust method to learn from the results.

There are the above and hundreds of other variables which are involved in determining email subject line performance, which makes measuring and optimising for each variable a tall order. There’s so much data, it’s hard for a human to comprehend it.

Luckily for you, that’s exactly what Phrasee does! Drop us a line to find out how we can help you maximise your email subject line performance.

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