We've all heard the oft-cited (and oft-debated) statistic that consumers' attention spans are shorter than those of goldfish.

Whether or not the measurement is accurate, it's hard to deny that attention spans are decreasing... or are they?

According to an analysis of billions of emails, summarized in an infographic, Litmus found that attention spans—at least when reading email—are increasing.

The email company found that the average time spent reading an email increased from 10.4 seconds in 2011 to 11.1 seconds last year. That may not sound like much, but it's a seven percent increase. Overall, more recipients are reading emails closely, and fewer are simply skimming them.

For highlights from the findings, and for tips on how to optimize your emails for short attention spans, check out the infographic. Just tap or click to see a larger version.