It is often suggested that project managers obtain three time estimates for work
ID: 442168 • Letter: I
Question
It is often suggested that project managers obtain three time estimates for work units that have significant uncertainty associated wiht their time estimates. Assume you have collected three time estimates for each activity for a performance monitoring system at an international airport baggage handling system. Your cost estimate worksheet suggests the following:
Project estimate: 50 hours
Project standard deviation: 18 hours
Based on this information and assuming 3 standard deviations from the mean to include approximately 99.75% of the area under the normal distribution curve, calculate:
a. project highest credibel hours
b. project lowest credible hours upper confidence limit
c. project lowest credible hours lower confidence limit
Explain to the airport executives, your primary sponsors, what these numbers mean.
Explanation / Answer
A)
50+3x18 = 104 hours
B)
50-3x18 = -4 = 0 hours(As time can’t be negative)
50+3x18 x sqrt(3) = 81.1769 hours
C)
50-3x18xsqrt(3) = 18.8231 hours
D)
The above numbers give us plenty of information regarding the project. We can say that 99.75% of the project’s time falls within 0 to 104 hours. Therefore these two are the most credible lowest and highest credible hours.
On the other hand the 99.75% confidence interval is (81.1769 hours, 18.8231 hours) so 99.75% of the project’s mean completion time falls within this time limit.
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