When you are ahead in a run situation, you will win more times than not. So, should you always double when you need to, and conversely how often should you accept a double when slightly behind in a run?
Puckish: A very simple rule works fine in most situations. If on roll you are 10% (of your pip count) ahead minus 2 pips, you have a borderline double. If you are 10% ahead plus 2 pips, your opponent has a borderline take/pass.
That is of course in "money play". The take point can be different in function of the match score (and the presumed strength difference between the opponents) ; and when one of the opponents has too many checkers on low points.
nabla: good point on the low points, you need to basically add pip counts for checkers on the 1 or 2 point to be accurate. Alternatively you can look at the number of average moves left and calculate the odds variation, but that gets complicated.