Rational or Random? Model Shows How People Send E-Mails

Nov 19, 2008
Luís Amaral. Photo by Andrew Campbell

In the last 10 years, e-mail has gone from a novelty to a necessity. What was once a pastime is now an essential form of communication, with many people opening their inboxes to find dozens of e-mails waiting.

But how do people respond to those e-mails? Do they act rationally, responding to the most important first, making sure the process is efficient? Or do they send e-mails randomly, when they are at their computers or when they have time, without any regard to efficiency?

These are questions that Luís Amaral, associate professor of chemical and biological engineering in the McCormick School of Engineering and Applied Science at Northwestern University, and his collaborators set out to answer. After studying e-mails sent and received from more than 3,000 e-mail accounts at a European university during a three-month period, they created a mathematical model that shows people send e-mail randomly, but in cycles.

The findings are published online by the Proceedings of the National Academy of Sciences.

Amaral said he was inspired to create such an e-mail model after a recent paper said that the rational model -- where people respond to e-mails in the most efficient way -- was the correct model.

"I was not convinced, since I don't do it in a rational way," he said. But if a random model was correct, there would be a typical interval between e-mails -- which, when Amaral looked at the data, wasn't the case. He wondered if it was possible for people to send e-mail randomly but still have non-random intervals where they didn't send e-mail.

The answer, it turned out, was fairly simple: People don't send e-mails when they are sleeping.

"During the day, you send e-mails, but then you go home, or go away for the weekend, and you don't send e-mails," he said. "These data were from a few years ago, and in Europe, this was especially the case, since many people didn't have the Internet at home."

The result was a model in which people send e-mails at random, but the probability of them sending e-mails during a given period depended on what that period was. If it was in the middle of the night, the probability was near zero. If it was during the weekend, the probability was much lower than during weekdays.

"The model explains all the data, and it shows that people have cycles in which they use certain services," Amaral says. "You can then make predictions based on those cycles to know when people are going to request a service. Even though it's random, there are peaks in demand that don't look random."

Other businesses and services could use such a model.

"If you know how people access that service, you can better plan how much capacity you need, when you need it, and how to best engineer your system to supply that capacity," Amaral said. "It also teaches you how to interact with the system -- a good time to send an e-mail is just about the time that the person has arrived at work."

Source: Northwestern University

Explore further: Voice, image give clues in hunt for Foley's killer

add to favorites email to friend print save as pdf

Related Stories

Researchers aim to thwart targeted cyberattacks

Aug 13, 2014

When it comes to Internet attacks, hackers have traditionally taken a blanket approach, sending out malware to large, random groups of people and hoping that something would stick. But in recent years, the ...

Publish don't perish thanks to new iPhone app

Aug 08, 2014

A new app developed at the University of Otago is already helping researchers in over 20 countries connect more effectively with journals that could publish their research.

Recommended for you

Voice, image give clues in hunt for Foley's killer

13 minutes ago

Police and intelligence services are using image analysis and voice-recognition software, studying social media postings and seeking human tips as they scramble to identify the militant recorded on a video ...

Smartphone-loss anxiety disorder

55 minutes ago

The smart phone has changed our behavior, sometimes for the better as we are now able to connect and engage with many more people than ever before, sometimes for the worse in that we may have become over-reliant on the connectivity ...

Why conspiracy theorists won't give up on MH17 and MH370

Aug 20, 2014

A huge criminal investigation is underway in the Netherlands, following the downing of flight MH17. Ten Dutch prosecutors and 200 policemen are involved in collecting evidence to present at the International Criminal Court in the Hague. The inv ...

Here's how you find out who shot down MH17

Aug 20, 2014

More than a month has passed since Malaysia Airlines flight MH17 crashed with the loss of all 298 lives on board. But despite the disturbances at the crash site near the small town of Grabovo, near Donetsk ...

Assange talks of leaving embassy, sowing confusion

Aug 18, 2014

WikiLeaks founder Julian Assange sowed confusion Monday with an announcement that appeared to indicate he was leaving his embassy bolt hole, but his spokesman later clarified that that would not happen unless ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

moj85
5 / 5 (1) Nov 19, 2008
Yet another wonderful article analyzing something that we already know: people don't send emails when they're asleep.
physpuppy
5 / 5 (1) Nov 19, 2008
people don't send emails when they're asleep.


Hmmm, why not? Judging by some comments on this site, I think some people post while asleep, so why couldn't they email in that condition as well? (turn the rank filter off and check out the posts rated "1" or "2" and see what I mean :-) )

gmurphy
not rated yet Nov 20, 2008
lol