Very few people give you a 50/50 estimate when you ask for a task duration. Unless you train the estimators each person will give you their personal estimate based on his/her risk tolerance. It might be a 90% estimate from Ms. Risk Averse and a 30% estimate from Mr. Everything’s Easy.
I know that you can give the same set of drawings and infromation to multiple people and you will get different answers from everyone, but I am not sure that I think estimating to a 50% chance of meeting a deadline really works in our world where the deadline is less than flexible. This creates the challenge in estimating hours - it is easy to estimate a safe number of hours that will allow you to get the job done. And if you are held to the hours that are estimated, the hours will naturally lean towards less risk. It is hard to estimate tightly - where there is enough hours to complete, but the hours must be efficient and effective.