Friends and clients of Silverpop know that we love to do studies. One of our recent projects was to review a random and anonymous sample of our clients' subject lines to find which characteristics drove the highest open rates.
We did some initial research to understand the trends behind open rates. What did we find? Only one thing seemed to drive a statistically significant difference in open rates. It wasn't subject line length. It wasn't the use or avoidance of certain words. It wasn't even the use of promotions or sales.
In fact, the only thing that materially affected open rates was the sender: the name of the company or person in the "from" line.
I've long been an advocate of Email Brand Value (EBV). I even dedicated a chapter to it in my book. But it was still a pleasant surprise to learn that EBV completely overshadowed everything other element of the subject line when it came to getting recipients to open a message.
I feel obliged to mention that these findings came from an initial review of the data. It's quite possible that the full study might have uncovered some additional drivers of open rates. However, the initial review was so clear that we didn't think it was worth completing the study. Also, to address some of the other studies I've seen on subject line attributes and open rates, I suspect the bigger impact of length and key words comes from email campaigns that are more about prospecting, and where there is no real brand relationship in place. Silverpop clients rarely do email prospecting / list rental, so we don't have data on how subject line attributes affect open rates.