What subject lines to use in email marketing? Simple or complex?

What subject lines to use in email marketing? Simple or complex?
When it comes to writing a subject line, most marketers aim well-known method of "KISS".

However, a study recently made by Touchstone discovered that blind dedication to this cause may be the reason that most recipients will not read your email.

Using their new virtual test technology recipients, instead of the real subscribers, Touchstone found that the more complex it is the language used, the clicks and open rates will be higher.

Some information about this study:


For this studio, Touchstone 2 methods used.

The first method  has been using Coleman-Liau Indexwhich is based on the number of characters in a word, not the number of syllables.

 The second method was Automatic index ReadabilityWho, like Coleman-Liau Index, primarily the number of characters used to assess intelligibility of part of the text.

Then, the text is classified by the American cataloging system, ranging from being easily understood by a child from kindergarten to the level of a university student.

Other methods can use the number of syllables of a word to define complexity, but Touchstone algorithm is currently not programmed to think in terms of syllables.

Examples of topics:

Classes 2 - 3

  • Gift certificates - Friday and Saturday

  • Great discounts on airfares

  • Do not miss the special offers

Classes 6 - 7

  • You qualified! Because you are a subscriber, your discounts at top destinations

  • Are you tired to always look tired?



  • Delicate, effect - odor neutralizing perfume Fragrance Spheres just $ 5.49

  • Swimwear at a price friendly prom awkward moments and more

What was found

The study involved analysis Touchstone 67 000 5. subjects and the result 41 billion emails sent.

Firstly, all the subjects in the database were classified according to the intelligibility using the 2 methods before determining whether the complexity of the language had an impact either on open rates or on rates clickthrough or be on rates click-to-open.

The gray bars in the chart below is also how many of each type emails were sent:



In the best practice guidelines for the composition of topics marketers are advised to keep topics as simple as possible. However, most emails are sent with subjects with a level of intelligibility for people aged between 9 and 14 years.

However, as the graph above shows, the average rate of openings, clicks and click-to-open sites tend to improve the complexity of the language.

In fact, subjects that were best were those of a person with a vocabulary of 16 - 18 years.

What can we learn?

This study not only suggests that the complexity of the language lead to better interaction with email, but also demonstrates once again the value of testing and optimization.

It's easy for marketers to assume that they know which language is more appealing to their customers.

But to have the best results, deserve to use one of many available tools for email marketing to enhance testing and optimization of the email message.

Not just saves time and resources, but the results will lead to greater involvement from customers.

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