How a more specific subject line affects opens, clicks, and conversions Experiment ID: #9553


Experiment Summary

Timeframe: 10/16/2018 - 10/24/2018

In this email experiment, the original subject line posed a question that would be completely normal to receive from a colleague at this time of year…”How are your year-end plans coming?” It felt personal and genuine, but we wondered if it wasn’t doing enough to prime recipients for the upcoming call-to-action. So for the treatment, we created an subject like that maintained the personal nature (using the word “you”) and increased the specificity and clarity around what the content of the email was ultimately leading towards. For the treatment, we said “A new year-end fundraising webinar for you”.

Research Question

Will a more specific subject line lead to greater email performance?


C: How are your year-end plans coming?
T1: A new year-end fundraising webinar for you


Treatment Name Click Rate Relative Difference Confidence
C: How are your year-end plans coming? 4.2%
T1: A new year-end fundraising webinar for you 6.0% 42.7% 100.0%

This experiment has a required sample size of 1,164 in order to be valid. Since the experiment had a total sample size of 7,814, and the level of confidence is above 95% the experiment results are valid.

Flux Metrics Affected

The Flux Metrics analyze the three primary metrics that affect revenue (traffic, conversion rate, and average gift). This experiment produced the following results:

    42.7% increase in traffic
× 0% increase in conversion rate
× 0% increase in average gift

Key Learnings

As we’ve seen in the past, even when the subject line doesn’t affect the open rate, it can still have a dramatic effect on downstream metrics. In this case, the open rate remained nearly identical – 36.14% vs 36.16%. But the treatment version increased clicks to the webinar registration page by 42.7% at a 99% level of confidence.

The treatment also increased webinar registrations by 18.8% and was approaching statistical validity at an 89% level of confidence. This shows us 2 important learnings:

1 – The subject line has a powerful effect on how recipients view and respond to the entire email, even if it makes no difference in the open rate.
2 – A subject line that makes a clear tie to the ultimate call-to-action has a greater chance of getting a click and a conversion.

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Experiment Documented by...

Nathan Hill

Nathan is an Optimization Evangelist at NextAfter. If you have any questions about this experiment or would like additional details not discussed above, please feel free to contact them directly.