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Bottom-Up (Micro)
• Single-Point Estimation • Three-Point Estimates • Multiple Estimators • Delphi Technique
1. Have people familiar with the tasks make the estimate.
2. Use several people to make estimates.
3. Base estimates on normal conditions, efficient methods, and a normal level of resources.
4. Use consistent time units in estimating task times.
5. Treat each task as independent, don’t aggregate.
6. Don’t make allowances for contingencies.
7. Adding a risk assessment helps avoid surprises to stakeholders.
Estimating Guidelines for Times, Costs, and Resources
Single Point Estimation
30 Days to Complete
How long will Task A take to complete?
Bottom-up (Micro)
Three-Point EstimatesHow long will Task A take to complete?
Optimistic (a) 20 daysMost Likely (m) 30 daysPessimistic (b) 58 days
Three-Point Estimates
Optimistic (a) 20 daysMost Likely (m) 30 daysPessimistic (b) 58 days
How long will Task A take to complete?
20 Days + 30 Days + 58 Days3 Estimates
= 36 days
Triangular Distribution or simple average
Activity Time Calculations
weighted average activity time
=Te
Activity Time Calculations
Te a + 4m + b 6
=
Three-Point EstimatesHow long will Task A take to complete?
te 20+ 4*30 + 58 6
=
Optimistic (a) 20 daysMost Likely (m) 30 daysPessimistic (b) 58 days
Three-Point EstimatesHow long will Task A take to complete?
te = 33.00 days
Optimistic (a) 20 daysMost Likely (m) 30 daysPessimistic (b) 58 days
Beta Distribution
Optimistic (a)
Like
lines
s or
Pro
babi
lity
—>
Most Likely (m)
Pessimistic (b)
te
Beta Distribution
Optimistic (a)
Like
lines
s or
Pro
babi
lity
—>
Most Likely (m)
Pessimistic (b)
33.00 days
Three-Point Estimates
Estimated Project Duration: 243 days
Probably that project will be done in 250 days: 74%
PERT Analysis
Multiple EstimatorsBottom Up Estimating
Estimator 1 Estimator 2 Estimator 33
20 Days 30 Days 50 Days
Bottom-up (Micro)
Multiple EstimatorsBottom Up Estimating
Estimator 1 Estimator 2 Estimator 33
20 Days 30 Days 50 Days
Bottom-up (Micro)
Multiple EstimatorsBottom Up Estimating
20 Days
Estimator 1 Estimator 2 Estimator 33
20 Days + 30 Days + 50 Days3 Estimators
= 33.3 Days
Bottom-up (Micro)
30 Days 50 Days
Delphi Technique
Multiple Estimators
Estimator 1 Estimator 2 Estimator 3
30 days
3
Bottom-up (Micro)
Bottom-Up (Micro)
• Single-Point Estimation • Three-Point Estimates • Multiple Estimators • Delphi Technique
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