Why hasn't he/she replied yet?

The paper, "Evolutions of Conversations in the Age of Email Overload, " by doctoral student Farshad Kooti, and Kristina Lerman, Research Associate professor in the USC Viterbi School of Engineering's Computer Science Department and a project lead of the USC Information Sciences Institute, along with colleagues at Yahoo! Labs, was presented at the World Wide Web Conference. The paper is the largest study of email to date, measuring how the volume of incoming email affects behaviors of recipients and the length of time it takes them to reply to emails. The study was conducted in accordance with privacy standards: individuals opted in to the study, the data was anonymized, and the emails were not read by humans.

Why isn't he/she responding yet? The researchers indicate a variety of factors are in play. While you may be obsessing if an email never arrived or has gone into someone's spam file, you should note, the researchers say 90 percent of people respond within a day or two of receiving an email to which they plan to respond. The most likely reply time is two minutes, and half of responders will respond in just under an hour.

Age is also an indicator for email response time. Younger people reply faster, but write shorter replies. Teens were the quickest, with an email response time-an average of 13 minutes. Young adults aged 20-35 years responded on average of 16 minutes of receiving an email. 35--50 year olds tended to respond in 24 minutes, on average. However, those over 51 years of age, on average took 47 minutes to respond.

While there was no major difference along gender lines, you might have to wait about 4 minutes longer for an email response from a woman than an email response from a man.

The platform also plays a critical role: If someone is working from a laptop, on average it will take them almost twice as long to respond than if he/she were using a mobile phone.

Is there a meaning behind that curt email response? As more people communicate via email, we try to read between the lines on the screen. Turns out that it's nothing you said or did. Emails with only five words are the most common. More than half the email replies are less than 43 words, and only 30 percent of emails are longer than 100 words.

When not to expect a response:

The researchers are also able to predict when an email thread will fizzle out. When users first email each other, they mimic each other with regards to the length of emails, but as the email chain continues, this synchronicity drops off. In general, users are synchronized until the middle of the conversation. The researchers identify telltale signs that the person with whom you are emailing isn't going to respond again. A long delay in the final response signals to both parties that the conversation is probably over.

How much is too much?

What happens when consumers have too many emails? It's not a shocker, younger users can cope with the increased email load more than older email users. When younger users become more overloaded they tend to send shorter and faster replies to cope with the increased load. On the other hand, older people respond to an increased load of emails by replying to a smaller fraction of emails.

Guidelines for Emailing:

The researchers find that in general, users are not able to keep up with the rising tide of emails. As email loads increase, users reply to a decreasing faction of emails. The researchers' work has implications for generating effective and engaging email interactions.

Though most of us are plugged in 24/7, there are optimal times to send emails. The researchers claim email responses follow a circadian rhythm -- people are more active on email during the day than at night. Furthermore, emails on weekends get shorter replies than weekdays. If you want a longer and perhaps more thoughtful reply, email someone in the morning. The researchers found that emails sent in the morning tend to get longer replies than those in the afternoon.