There's nothing like firing off a carefully crafted e-mail and then waiting for what seems like an eternity for a reply. When you finally do get an answer, you might still be frustrated. What do you make of the fact that it is only 10 words long?

We now have some clues about typical e-mail response patterns, thanks to a recent study drawing on 16 billion e-mails sent by more than two million people. The participants were Yahoo Mail users who allowed their anonymized data to be used in what appears to be the largest-ever analysis of e-mail behavior. The researchers, based at the University of Southern California and Yahoo Labs, used algorithms to mine data about the times messages were sent and the number of words they contained, among other factors. Here are some of the surprising revelations:

  • The most likely length of a reply is just five words.
  • More than 90 percent of replies are sent within a day.
  • The younger you are, the faster and more terse your reply (box at bottom).
  • Messages sent on weekday mornings got the fastest responses.
  • E-mails with attachments took twice as long to get a reply as those without.

The researchers included only users who wrote to one another at least five times in the months covered by the study period. After mining the data, the researchers found they could use their algorithm to predict when an e-mail conversation was nearing its end. For the first half of a dialogue, correspondents usually developed similar reply times and e-mail lengths, lobbing messages back and forth at a regular clip. Yet that similarity decreased as the conversation trailed off. Many conversations ended with a long lag before one correspondent sent a final brief reply.

Of note to the anxious e-mailer: the more words in a reply, the longer it tended to take for the writer to send it—but only up to 100 words. Beyond that, the time for a reply actually dropped slightly, except for in the oldest age group. So if you're expecting a hefty reply to your mission-critical missive, it won't necessarily take any longer than a 100-word message. That may be some comfort while you wait on the edge of your seat.

median reply time/length