When asking your online community to share with friends by email, what default subject line should you use? Although this seems like a small question, the subject line will be the first thing their friends see and can have a huge impact on how likely people are to read, engage, and click back to your website.

What types of subject lines work best for sharing petitions by email? CREDO Action used the ShareProgress platform to answer the question by running seven different experiments on their petitions that tested descriptive subject lines (e.g., “Tell Obama: Justify your indiscriminate spying on Americans”) versus more personal subject lines (e.g., “I just signed this — will you?”).

Personal subject line consistently outperformed more descriptive ones. In every case, emails with personal subject lines got at least 30% more people to sign a CREDO Action petition, and in one case, the increase was over 90%!

You can see the results from seven different share email subject line tests that CREDO ran in the following spreadsheet:

Success Rate = # of emails shares that generated actions / Total # of email shares

With these results, we can conclude that personal subject lines for share emails are a fairly clear best practice for organizations running online petitions. It’s difficult to say whether this can be generalized for sharing articles, videos, or even other types of online actions, though, since the mindset of people receiving share emails may lead to different behavior in these cases. At the very least, the results from CREDO share emails show that personal subject lines are worth testing more widely. Luckily, with ShareProgress, you’ve got an easy way to do just that.