How subject line personalization affects open rate

Experiment ID: #5694


CaringBridge offers free personal, protected websites for people to easily share updates and receive support and encouragement from their community during a health journey. Every 7 minutes, a CaringBridge website is created for someone experiencing a health event.

Experiment Summary

Timeframe: 11/22/2016 - 11/23/2016

CaringBridge was running a fundraising campaign around Mother’s Day. Their email appeals typically came from Sona Mehring, their founder.

As part of a Mother’s Day fundraising campaign, they wanted to test a different approach, sending an email from a user of the site. They hypothesized that this personal approach would result in more donations. However, they knew they would have to bridge the relational gap between the new sender and the recipient, and they believed this could be done by maximizing personalization.

Their new treatment, included personalization in the subject line with the first name of the recipient. It also included personalization in the first few lines of the copy, which came through in the preview text.

They split the file and launched an A/B test to determine a winner.

Research Question

Will a personalized subject line increase open rate?


C: Founder + Campaign Headline
T1: Donor + Personal Headline


 Treatment NameOpen RateRelative DifferenceConfidence
C: Founder + Campaign Headline 7.6%
T1: Donor + Personal Headline 18.1%137.2% 100.0%

This experiment has a required sample size of 79 in order to be valid. Since the experiment had a total sample size of 195,554, 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:

    137.2% increase in traffic
× 0% increase in conversion rate
× 0% increase in average gift

Key Learnings

The treatment subject line, despite the unfamiliar sender, produced a 137.2% increase in open rate. This implies that personalization in the subject line is a powerful trigger that can effectively bridge a gap between an unknown sender and a recipient.

Experiment Documented by Jeff Giddens
Jeff Giddens is President of NextAfter.

Question about experiment #5694

If you have any questions about this experiment or would like additional details not discussed above, please feel free to contact them directly.