Being a bit geeky, one of the things I like to do is analyse data. And one analysis I often return to is effective email subject lines.

Now the ultimate measure of the performance of an email is how much new business I get as a result of my emails. But that can be tricky to track down to individual emails.

And in truth, the effect of the emails is culmulative rather than one email suddenly causing someone to pick up the phone and hire me or buy a product.

So what I often analyse is email open rates. What percentage of people who receive each email actually open it. So it's a measure of the performance of the email subject line rather than the email as a whole.

If I look at the emails you've been getting every Sunday from me there are some pretty interesting results that may help you when you're trying to write emails to get them opened by your potential clients.

Generally speaking, email open rates go down over time.

The first time I email someone after they sign up for my newsletter there's a high chance they'll open it and read it. Over time, people's interests and priorities change so the open rates go down.

What I looked for was email subject lines that “bucked the trend”. That got significantly higher opens that the email that preceded them.

Here are my three best performing subject lines using this criteria:

“5 crippling beliefs that keep consultants and coaches in the poor house”

“How to escape marketing overwhelm”

“Business Development romance in practice”

Why did they perform so well?

The first two are obvious, I think.

The first promises to reveal some information on “crippling beliefs” likely to “keep you in the poor house” if you hold them. The language is strong, and the benefit is clear: avoid these beliefs to avoid ending up poor.

The second promises to show you how to avoid a problem I believe a large number of professionals suffer from: being overwhelmed with their marketing. It's likely to hit a raw nerve with many people and again, the word “overwhelm” is a strong one.

The third one is a bit of a puzzle. It doesn't quite fit into the pattern of promising a strong benefit.

My belief is that the high open rate is driven by curiosity. People wondering what on earth “business development romance” actually is.

So three quite different types of subject line. One on avoiding potential pain people could be worried about. One on alleviating pain they could well be already feeling. And one arousing their curiosity.

When you come to write your own emails, see if you can work some of those themes into your subject lines.

And feel free to “steal” my subject lines too and tweak them for your own use. The “5 crippling beliefs” one was actually adapted from a headline on a Copyblogger blog post.