Tuesday, November 1, 2011

How do predictions affect completion time?

At any given moment, I have a lot of different things going on.  I’m often working with a number of different colleagues and students on research projects and papers.  I try to write entries for this blog regularly.  I edit a journal, and I have to read papers and write letters of acceptance or rejection. 

When I’m working with other people, it is often important for me to make predictions about when I will be finished with a part of the task that I have taken on.  These estimates allow my colleagues to make plans about when to expect my work and when they should plan to do their share of the project. 

Like most people, though, my predictions are often too optimistic.  That is, I’m sure that I’ll get things finished before I actually do.

An important question about these predictions, though is whether they affect how quickly you actually get things done.  That is, your prediction about when you will complete something may be rosy, but perhaps that rosy prediction actually  helps you get things done faster. 

This question was addressed in an interesting paper by Roger Buehler, Johanna Peetz, and Dale Griffin in the January, 2010 issue of Organizational Behavior and Human Decision Processes. 

They found that whether a prediction affects when you will complete a task depends on whether that task is “closed” or “open.”  A closed task is one that is generally completed in a single setting.  An open task is one that requires a number of steps that generally can’t be done at once.  Often open tasks are more complex than closed ones, but they don’t have to be.  For example, framing a photo you took on your digital camera is fairly easy.  First you print the picture, then you buy a frame that fits it, then you put the picture in the frame.  All told, it may take an hour of your time to complete the task.  Chances are, though, you will print the picture at one time, buy the picture frame at another time, and put it in the frame at yet a third time.

The results of their studies demonstrated that people’s predictions about deadlines affected when they started on the first of the tasks they had to perform.  People would begin the task earlier when they made an earlier prediction of when they would finish than when they made a later prediction.  So, for closed tasks that required just one sitting to complete, they would also finish them faster.  For open tasks, they would start the task faster if they made an earlier prediction than if they made a later prediction, but because the task involved multiple steps, they would not actually complete the task faster.

Let me step through one of the studies, because the methods they used were interesting.  In one study, they asked people to write three short stories from their home and then send it to the experimenters.  In the closed version of the task, the stories could be typed on a word processor and then emailed.  In the open version of the task, the stories had to be typed, printed out, and then mailed.   The open version of the task required putting the stories in an envelope, buying a stamp and mailing them, so it would probably involve at least two different steps.

To manipulate people’s predictions, they were given a time line starting with today and ending with the due date for the stories two weeks in the future.  To get people to make early predictions, they were asked to start at today and look forward on the time line and mark on the line when they would complete the assignment.  To get people to make late predictions, they were asked to start at the deadline and work backward and mark when they would complete the assignment.  This technique got the “early” people to make a significantly earlier prediction than the “late” people.

Consistent with the authors’ predictions, when people just had to email the stories, those who made early predictions sent in the stories earlier than those who made late predictions.  When people had to send the stories by mail, though, the effect went away.  The stories were sent in at about the same time regardless of the prediction.   

These studies suggest that there may be some value in making rosy predictions.  Being optimistic about when you will finish a task does help you to start it earlier.  But if a task is open-ended, you still need to be vigilant about completing all of the steps of that task.