© Copyright LEXTA GmbH 2006 On the difficulties in determining effort estimation accuracy in...
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Transcript of © Copyright LEXTA GmbH 2006 On the difficulties in determining effort estimation accuracy in...
© Copyright LEXTA GmbH 2006
On the difficulties in determining effort estimation accuracy in practice
MeLLow Workshop
Ursula Löbbert-Passing
October 17-18, 2006
Accuracy_v2.ppt
Exhibit 2
In the IT Management lifecycle, LEXTA covers benchmarking, cost cutting and sourcing as well as professionalising processes and projects
LIFECYCLE IT MANAGEMENT
IT Benchmarking
Professionalising IT processes
IT Sourcing
IT Cost Cutting
ProfessionalisingIT projects
Accuracy_v2.ppt
Exhibit 3
Estimation accuracy is considered as THE quality criterion for an estimation method
ActualActualPlan
Accuracy
• The most common formula for determining effort estimation accuracy (in percent) in practice is
• Positive value = Over-estimation
• Negative value = Under-estimation (budget overrun)
Accuracy_v2.ppt
Exhibit 4
Estimation accuracy is determined by comparing values from different points of time
Project execution
Estimation Measurement of
actual effort
Project lifetime
Unexpected event
(e. g. requirement shift)
Comparison:
Estimation accuracy
t
Accuracy_v2.ppt
Exhibit 5
Four factors “dilute” the effect of the estimation method on estimation accuracy
Information gapFaulty measurement of actual effort
Project management
Unexpected events
Estimation method
Estimation accuracy
Accuracy_v2.ppt
Exhibit 6
All factors contribute jointly to estimation (in)accuracy
Factor Contributes to estimation (in)accuracy, because
Estimation method
• Method takes/does not take all relevant information into account (parameters, number of aspects an expert can consider)
• Method produces (in)correct conclusions from available information (e. g. by model assumptions, extent of expert experience)
Information gap • At time of estimation, available project information (requirements, architecture, team etc.) is incomplete assumptions necessary
• At time of actual effort measurement, more (complete) information is available “Information gap”
Project management
Project management influences actual effort, e. g. by (in)efficient coordination of activities and teams „Parkinson’s Law“
Unexpected events
Unexpected events lead to unexpected effort „Information gap“ between time of estimation and time of actual effort measurement Strictly, estimated and measured effort are not comparable any more
Faulty measure-ment of actual effort
Measured effort is not necessarily the actual effort due to
• Manipulation of measured effort: Incentive exists when employees are evaluated by their estimation accuracy
• Faulty measurement: When actual effort does not “fit” into the measurement scheme (e. g. project phases), it may be booked somewhere non-appropriate Effort measured for one measurement category (e. g. one phase) is not necessarily the actual effort
• No measurement of overtime Measured effort is too low
„Noise“
Accuracy_v2.ppt
Exhibit 7
There are remedies to exclude three of the „noise“ factors
Information gapFaulty measurement of actual effort
Project management
Unexpected events
Estimation method
Estimation accuracy
Document input information for
estimates and update regularly
Update estimates after unexpected
events
Assure quality of effort measurements
• Do not evaluate employees based on their estimation accuracy
• Match structures of effort measurement and estima-tion templates
• Measure overtime
• Ex-post estimates are often recommended but imprac-tical in practice (extra effort)