Someone come up a formula:

 It factors the person's expectancy for succeeding at a given task (E) or self-confidence; the value of completing the task (V); its immediacy or availability (Gamma); and the person's sensitivity to delay (D) to come up with the desirability of the task (Utility).

The equation reads: Utility = E x V / (Gamma) x D.

http://news.com.com/2100-1008_3-6149636.html?part=rss&tag=2547-1_3-0-20&subj=news

Quite true to me