The understanding of the three-point estimation Method--soft test

The three-point estimate is also called PERT, which calculates the duration of each activity with three possibilities, calculates the most pessimistic duration, the most likely duration, the most optimistic duration, and then calculates the expected duration of the activity, and the PERT method calculates the expected duration.
To calculate the duration with the PERT method, we must remember the following three formulas (p represents the most pessimistic duration; M represents the most probable duration; O represents the most optimistic duration)
PERT Formula



Standard deviation formula: (A+4M+B)/6


Variance formula: (B-A)/6


The PERT formula calculates the average duration of an activity, that is, 50% of the probability is completed within that duration. With normal statistical distribution, the probability of the duration falling within the 1 standard deviation range of the average duration is 68.26%, the probability of 2 standard deviation is 95.46%, 3 standard deviation probability is 99.73%, this three probability must remember, if we use 1 standard deviation to estimate the duration, that duration is in the average duration plus/ Minus 1 in the range of standard deviation. The other same.


Knowledge point 1: Three point estimation method


Routine Test 1: Complete activity A pessimistic estimate 36 days, most likely estimate 21 days, optimistic estimate 6 days, ask for the expected completion time of the activity.


Comments: The earliest form of assessment, the simplest, rote formula can be.




Routine Test 2: Complete activity A pessimistic estimate 36 days, most likely to estimate 21 days, optimistic estimate 6 days, seek standard deviation.


Comments: The current assessment of the form, relatively simple, remember the formula and probability number can (official)








Routine Test 3: Complete activity A pessimistic estimate 36 days, most likely estimated 21 days, optimistic estimate 6 days, activity A in 16 days to 26 days to complete the probability is how much.


Comments: The current form of assessment, slightly difficult, according to the standard deviation and range of activities to determine the standard deviation interval, and then judge the probability.


Write the formula and the probability number (no probability in the official textbook)




Depth Test 1: Completed activity A pessimistic estimate 36 days, most likely estimated 21 days, optimistic estimate 6 days, ask:


(1) What is the probability of completion within 16 days?


(2) What is the probability of completion within 21 days?


(3) What is the probability of completion after 21 days?


(4) The probability of completion between 21 days to 26 days.


(5) The probability of completion in 26 days is how much.


This algorithm is a pert estimate
Final estimate result = (pessimistic duration + optimistic duration +4x most likely duration)/6
Standard deviation = (pessimistic-optimistic)/6
Bring into the company plan PERT estimates are as follows: (36+21*4+6)/6=21
The standard deviation of the formula is: (36-6)/6=5
So according to the positive distribution: 16 (21-5) ~26 (21+5) The probability of this interval range is 68.26%. Note: The probability of a standard deviation in plus or minus is 68.26%
The probability of 16~26 this interval is calculated, with a probability of 100%-this interval of 68.26% to get the probability of not in this interval (100%-68.26%=31.74%),
After 31.74%, the probability divided by 2 is less than 16 days and more than 26 days, respectively, the corresponding probabilities (31.74%/2=15.87%)
So:
(1) What is the probability of completion within 16 days? --15.87% ((100%-68.26)/2=15.87%)
(2) What is the probability of completion within 21 days? --50% (μ=21, so exactly 50%)
(3) What is the probability of completion after 21 days? --50% (μ=21, so exactly 50%)
(4) The probability of completion between 21 days to 26 days. --68.26% (the probability of a standard deviation of positive and negative is 68.26%)
(5) The probability of completion in 26 days is how much. --84.13% (100%-15.87%=84.13% or 50%+68.26%/2=84.13%)
Draw a map of the right too, look at the picture and you can see it.