[twelvechairs]

Estimation depends on the unknowns which you can typically put down to overall task time and complexity of the task. If its is something they have done before and a short task (hours), x1 is fine. If it is something new and long (weeks), x5 may be underselling it.

Breaking down a long task to be as granular as possible then rating each component against a scale of how much experience/confidence you have is the best approach to managing risk. As a manager, if you aren't asking people to explain this, you should be.

I've never seen anyone do it (I also haven't worked anywhere massive), but monte-carlo analysis with a tornado chart etc. would be the best way of managing this kind of risk at a complex-systems scale. It is a system used by the top real-estate developers.