Method guideDecision Making

PERT Estimation

A practical method guide: clarify prerequisites and materials, understand the complete process, and look up outputs, pitfalls, and stop criteria.

ComplexityMedium

Time15-45 min

Participants1-8

FormatWorkshop + async

MaturityCanonical

Plan PERT Estimation

Prerequisite

What needs to be finished first

Complete firstComparable subject

Close work packages, unit, Done, and dependencies; explicitly check independence before aggregating variance.

Without a common frame, values are not comparable.

Complete firstEvidence access

Defined work packages, O/M/P scenarios, historical data, PERT worksheet, dependencies, and assumption log

Missing data remains visible as uncertainty.

Preparation

What needs to be ready before start

Materials

Defined work packages, O/M/P scenarios, historical data, PERT worksheet, dependencies, and assumption log

People / roles

Estimator · work owner · risk/data expert · schedule owner

Pre-read

Close work packages, unit, Done, and dependencies; explicitly check independence before aggregating variance.

Time needed

45–90 minutes for a small set of independent work packages; network scheduling separate.

Setup

Prepare a workspace with Scope · Values · Calculate · Aggregate · Interpret; separate example from live data.

Core question

The one question this method answers

What PERT expected values and variances follow from O/M/P, and how are independent work packages aggregated correctly?

Flow

Phases with goal, actions, output and pitfall

Optimistische, wahrscheinlichste und pessimistische Einschätzungen werden mathematisch gewichtet, statt einfach gemittelt zu werden. So entsteht eine Planungszahl, die Unsicherheit sichtbar mitführt und weniger von Extremwerten verzerrt wird. Nützlich ist vor allem die konsistente Verbindung von Schätzung und Risikobild.

PERT Estimation · working structure

Fictional example

Fictional values show the actual method fields.

PERT Estimation · working structure
Package	O / M / P	E = (O+4M+P)/6	SD = (P−O)/6	Variance	Dependency	Model limit
A · TokenisationAdd evidence and rationale.	4 / 7 / 16 days	(4+28+16)/6 = 8.00	(16−4)/6 = 2.00	4.00	Independent of B for example	Check shared certification
B · RolloutAdd evidence and rationale.	2 / 3 / 8 days	(2+12+8)/6 = 3.67	(8−2)/6 = 1.00	1.00	Independent of A for example	Rollout window fixed
AggregateAdd evidence and rationale.	Do not average again	8.00+3.67 = 11.67	√(4+1) = 2.24	5.00	Only under independence	No guaranteed interval

1. O / M / P
A · Tokenisation
4 / 7 / 16 days
B · Rollout
2 / 3 / 8 days
Aggregate
Do not average again
2. E = (O+4M+P)/6
A · Tokenisation
(4+28+16)/6 = 8.00
B · Rollout
(2+12+8)/6 = 3.67
Aggregate
8.00+3.67 = 11.67
3. SD = (P−O)/6
A · Tokenisation
(16−4)/6 = 2.00
B · Rollout
(8−2)/6 = 1.00
Aggregate
√(4+1) = 2.24
4. Variance
A · Tokenisation
4.00
B · Rollout
1.00
Aggregate
5.00
5. Dependency
A · Tokenisation
Independent of B for example
B · Rollout
Independent of A for example
Aggregate
Only under independence
6. Model limit
A · Tokenisation
Check shared certification
B · Rollout
Rollout window fixed
Aggregate
No guaranteed interval

All values are fictional.

Reference · original teaching example

1
Scope
PERT frame
Goal
PERT frame: Capture work packages, unit, Done, dependencies, and common risks.
Inputs for this step
- Close work packages, unit, Done, and dependencies; explicitly check independence before aggregating variance.
- Defined work packages, O/M/P scenarios, historical data, PERT worksheet, dependencies, and assumption log
Actions
- Capture work packages, unit, Done, dependencies, and common risks.
Output
PERT frame
Capture work packages, unit, Done, dependencies, and common risks.
Quality check
Are packages separable and common causes visible?
Pitfall
Dependent packages are calculated as independent. Mark dependencies and common risk drivers before using formulas.
Timing: 10–15 minutes
2
Values
O/M/P table
Goal
O/M/P table: Set O, M, and P per package as plausible scenarios with O ≤ M ≤ P.
Inputs for this step
- PERT frame
Actions
- Set O, M, and P per package as plausible scenarios with O ≤ M ≤ P.
Output
O/M/P table
Set O, M, and P per package as plausible scenarios with O ≤ M ≤ P.
Quality check
Do values describe one scope and explainable conditions?
Pitfall
M is a management target rather than the most likely scenario. Derive M from analogy and justify O/P with conditions.
Timing: 10–20 minutes
3
Calculate
PERT measures
Goal
PERT measures: For each package calculate E=(O+4M+P)/6, SD=(P−O)/6, and variance=SD².
Inputs for this step
- O/M/P table
Actions
- For each package calculate E=(O+4M+P)/6, SD=(P−O)/6, and variance=SD².
Output
PERT measures
For each package calculate E=(O+4M+P)/6, SD=(P−O)/6, and variance=SD².
Quality check
Are weighting, unit, and calculation visible?
Pitfall
PERT is confused with a simple triangular mean. Show formula beside each result and set rounding rule.
Timing: 10–15 minutes
4
Aggregate
Aggregate
Goal
Aggregate: Only under independence add expected values and variances; total SD is square root of summed variance.
Inputs for this step
- PERT measures
Actions
- Only under independence add expected values and variances; total SD is square root of summed variance.
Output
Aggregate
Only under independence add expected values and variances; total SD is square root of summed variance.
Quality check
Were variances rather than standard deviations added?
Pitfall
SD 2+1 is added as total SD 3. Sum variances; model correlation separately or state it as a limit.
Timing: 5–10 minutes
5
Interpret
Planning finding
Goal
Planning finding: Use measures with assumptions; do not claim confidence without a validated distribution.
Inputs for this step
- Aggregate
Actions
- Use measures with assumptions; do not claim confidence without a validated distribution.
Output
Planning finding
Use measures with assumptions; do not claim confidence without a validated distribution.
Quality check
Are model limits, risks, and review triggers recorded?
Pitfall
E±2SD is called a guaranteed 95% interval without validation. Check distribution/independence and use simulation for date forecasts.
Timing: 10–15 minutes

Artifact

What comes out at the end

Sketch: what the artifact looks like

PERT Estimation · gewichteter ErwartungswertOptimistischen, wahrscheinlichsten und pessimistischen Wert mit O plus 4M plus P geteilt durch 6 zu einer Planungsannahme verdichten

Form

PERT table with E=(O+4M+P)/6, SD=(P−O)/6, variance=SD², aggregated independent variances, and stated model limits.

Versioning / ownership

Record date, team, data state, and review date; preserve prior versions.

Tool alternatives

O/M/P scenario sheet
PERT worksheet
Dependency and assumption log

pert-estimation-working-template.md

Set subject, data, roles, flow, and review.

PERT Estimation: Worksheet

Question

To be confirmed

Desired outcome

To be confirmed

Scope

Complete run Time: 45–90 minutes for a small set of independent work packages; network scheduling separate.

Complete this worksheet on paper or in your own document during the work.

Preparation for this scope

Method setup

Materials: Defined work packages, O/M/P scenarios, historical data, PERT worksheet, dependencies, and assumption log
Roles: Estimator · work owner · risk/data expert · schedule owner
Advance information: Close work packages, unit, Done, and dependencies; explicitly check independence before aggregating variance.
Overall time needed: 45–90 minutes for a small set of independent work packages; network scheduling separate.
Setup: Prepare a workspace with Scope · Values · Calculate · Aggregate · Interpret; separate example from live data.

Prepare for the work steps

Scope: PERT frame

Close work packages, unit, Done, and dependencies; explicitly check independence before aggregating variance.
Defined work packages, O/M/P scenarios, historical data, PERT worksheet, dependencies, and assumption log

Values: O/M/P table

PERT frame

Calculate: PERT measures

O/M/P table

Aggregate: Aggregate

PERT measures

Interpret: Planning finding

Aggregate

PERT Estimation · working structure

Package	O / M / P	E = (O+4M+P)/6	SD = (P−O)/6	Variance	Dependency	Model limit
A · Tokenisation
B · Rollout
Aggregate

A · Tokenisation: Add evidence and rationale.
B · Rollout: Add evidence and rationale.
Aggregate: Add evidence and rationale.

The blank worksheet contains prompts only.

Reference · original teaching example

Scope: PERT frame

Expected artifact: PERT frame

Capture work packages, unit, Done, dependencies, and common risks.

Entry:

...

Are packages separable and common causes visible?

Values: O/M/P table

Expected artifact: O/M/P table

Set O, M, and P per package as plausible scenarios with O ≤ M ≤ P.

Entry:

...

Do values describe one scope and explainable conditions?

Calculate: PERT measures

Expected artifact: PERT measures

For each package calculate E=(O+4M+P)/6, SD=(P−O)/6, and variance=SD².

Entry:

...

Are weighting, unit, and calculation visible?

Aggregate: Aggregate

Expected artifact: Aggregate

Only under independence add expected values and variances; total SD is square root of summed variance.

Entry:

...

Were variances rather than standard deviations added?

Interpret: Planning finding

Expected artifact: Planning finding

Use measures with assumptions; do not claim confidence without a validated distribution.

Entry:

...

Are model limits, risks, and review triggers recorded?

Open questions and next steps

...

Method guide: https://methodatlas.meierhoff-systems.de/en/methods/pert-estimation/run-sheet

Example output

Concrete filled scenario, fictional example

Fictional example for orientation. Counts and timings describe this case and are not universal requirements.

pert-estimation-beispiel.md

Concrete filled scenario, fictional example

Fictional teaching example: PERT Estimation · working structure

Package	O / M / P	E = (O+4M+P)/6	SD = (P−O)/6	Variance	Dependency	Model limit
A · Tokenisation	4 / 7 / 16 days	(4+28+16)/6 = 8.00	(16−4)/6 = 2.00	4.00	Independent of B for example	Check shared certification
B · Rollout	2 / 3 / 8 days	(2+12+8)/6 = 3.67	(8−2)/6 = 1.00	1.00	Independent of A for example	Rollout window fixed
Aggregate	Do not average again	8.00+3.67 = 11.67	√(4+1) = 2.24	5.00	Only under independence	No guaranteed interval

Pitfalls

Recognize symptoms and steer against them

Quick overview, the full text is in the matching phase in the flow

PERT frameDependent packages are calculated as independent.View in phase
O/M/P tableM is a management target rather than the most likely scenario.View in phase
PERT measuresPERT is confused with a simple triangular mean.View in phase
AggregateSD 2+1 is added as total SD 3.View in phase
Planning findingE±2SD is called a guaranteed 95% interval without validation.View in phase

Stop criteria

When to pause, resolve prerequisites, or choose another approach

Stop Scope: Are packages separable and common causes visible?

Stop Values: Do values describe one scope and explainable conditions?

Stop Calculate: Are weighting, unit, and calculation visible?

Stop Aggregate: Were variances rather than standard deviations added?

Stop Interpret: Are model limits, risks, and review triggers recorded?

Where to go next?

Delivery

Monte Carlo Forecasting

Uses variance and dependencies for a simulation-based delivery distribution.

Decision Making

Risk Matrix

Formally assesses the open independence assumptions and uncertainties by likelihood and impact.

Finished the method guide?

Go to the profile for purpose, similar methods, and sources or continue to the next method in the catalog.

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PERT Estimation · working structure

1. O / M / P

2. E = (O+4M+P)/6

3. SD = (P−O)/6

4. Variance

5. Dependency

6. Model limit

PERT frame

O/M/P table

PERT measures

Aggregate

Planning finding

pert-estimation-working-template.md

PERT Estimation: Worksheet

Question

Desired outcome

Scope

Preparation for this scope

Method setup

Prepare for the work steps

Scope: PERT frame

Values: O/M/P table

Calculate: PERT measures

Aggregate: Aggregate

Interpret: Planning finding

PERT Estimation · working structure

Scope: PERT frame

Values: O/M/P table

Calculate: PERT measures

Aggregate: Aggregate

Interpret: Planning finding

Open questions and next steps

pert-estimation-beispiel.md

Fictional teaching example: PERT Estimation · working structure

PERT frame

O/M/P table

PERT measures

Aggregate

Planning finding

Where to go next?

Finished the method guide?