Chapter 10

Tip #47 

Decompose large estimates into small pieces so that you can take advantage of the Law of Large Numbers: the errors on the high side and the errors on the low side cancel each other out to some degree.

Tip #48 

Use a generic software-project work breakdown structure (WBS) to avoid omitting common activities.

Tip #49 

Use the simple standard deviation formula to compute meaningful aggregate Best Case and Worst Case estimates for estimates containing 10 tasks or fewer.

Tip #50 

Use the complex standard deviation formula to compute meaningful aggregate Best Case and Worst Case estimates when you have about 10 tasks or more.

Tip #51 

Don't divide the range from best case to worst case by 6 to obtain standard deviations for individual task estimates. Choose a divisor based on the accuracy of your estimation ranges.

Tip #52 

Focus on making your Expected Case estimates accurate. If the individual estimates are accurate, aggregation will not create problems. If the individual estimates are not accurate, aggregation will be problematic until you find a way to make them accurate.