Reference Class Forecaster

Reference Class Forecaster

When to use

Calibrate cost, duration, and benefit estimates using the outside view before inside-view narrative wins the room — capital projects, transformation programs, product launches, and M&A integration timelines.

Pairs naturally with /transformation:business-case, /corporate-strategy:evaluate-strategic-option, and /value-realisation:realisation-review calibration loops.

What this skill does not do

• Does not replace sponsor judgment — produces adjusted ranges and explicit bias flags; strategist decides funding.
• Does not invent a reference class — asks for comparables or uses sourced benchmarks; gaps tagged INPUT NEEDED.
• Does not approve spend — output is decision support with [review] on every adjusted headline number.

Preconditions

| Input | If missing | |---|---| | Inside-view estimate (cost, duration, benefit, or all three) | Ask — cannot forecast without a claim to calibrate | | Project type and scale band | Ask or infer from context; label assumption | | Comparable reference class (optional) | Build from user examples + tagged public benchmarks |

Provisional mode

When no org-specific track record exists in profiles, use published reference-class medians (Flyvbjerg infrastructure/program data, sector benchmarks) tagged [model knowledge — verify] and confidence structured first pass.

Trust spine

• Confidence bands (hypothesis-driven-analysis):
• High: ≥3 independent comparables in class; uplift applied with cited Green Book or org policy.
• Medium: 1–2 comparables or mixed quality; uplift stated with rationale.
• Low: Class named but thin evidence — directional adjustment only.
• Analytical Rigor (mandatory): Inside vs outside view shown side by side; uplift arithmetic explicit.
• Accountability gap: Adjusted range presented; inside-view retained for contrast — strategist picks which to fund against.
• Per ../../references/trust-conventions.md for sourcing, [verify], and GATE before board finals.

Assumption audit

| Assumption | Status | If wrong, what breaks | |---|---|---| | Reference class is comparable (scale, sector, delivery model) | [confirmed / partial / weak] | Outside view misapplied | | Inside-view estimate completeness | [full / partial / headline only] | Wrong dimension calibrated | | Org optimism-bias policy | [profile / Green Book default / user override] | Uplift % disputed | | Benefit vs cost/duration focus | [stated / inferred] | Wrong metric adjusted |

Red flags

Non-negotiable calibration rules:

• MUST NOT present a single-point inside-view forecast as defensible without an outside-view row — narrative planning causes systematic underestimation of cost and duration (Flyvbjerg).
• Do not proceed to High confidence without naming the reference class explicitly — unnamed classes cause apples-to-oranges calibration.
• Hard stop: applying zero uplift when inside view is below class median on benefits or above on cost/duration without written rationale — that is optimism bias unchecked.
• MUST NOT blend cost, duration, and benefit adjustments into one opaque haircut — show each dimension.

Outside-view step

This skill's core workflow is the outside view (Flyvbjerg) plus optimism-bias uplift (HM Treasury Green Book):

1. Name the inside view — restate the sponsor's estimate for cost, duration, and/or benefits exactly as given.
2. Define the reference class — 3+ comparable delivered projects/programs where outcomes are documented; tag each source.
3. Extract class statistics — median and P80 cost overrun, duration slip, and benefit realisation for the class (Flyvbjerg outside-view method).
4. Apply Green Book optimism-bias uplift — where inside view is more optimistic than class median on benefits or more pessimistic than median on risk, apply an explicit percentage uplift to costs/duration or haircut to benefits per Green Book guidance ("demonstrated, systematic tendency" for appraisers to be overly optimistic); state the % and policy basis.
5. Produce adjusted range — low / central / high with inside view retained for contrast.

Always show inside and outside views side by side because decision-makers anchor on the first number they see — presenting only the inside view tends to cause approval at an uncorrected optimistic estimate.

Workflow

Before step 1: Read and apply ../../references/trust-conventions.md — source-tagging, [verify] on model-only numbers, load-bearing assumptions at top, numbers provenance, confidence labeling, and board-ready gate.

1. Confirm project type, scale, and which dimensions to calibrate (cost, duration, benefit).
2. Run Assumption audit; halt on missing inside-view estimate.
3. Assemble reference class — user comparables first, then tagged public benchmarks.
4. Compute class medians and spread; document sources.
5. Apply Green Book optimism-bias uplift per dimension with explicit %.
6. Flag where inside view sits vs class (optimistic / aligned / conservative).
7. Run Red flags self-check before output.
8. GATE before board/exec final per trust spine.

Output format

CONFIDENCE: [defensible recommendation | structured first pass]
REFERENCE CLASS: [name — comparables listed with sources]

INSIDE VIEW (sponsor estimate):
| Dimension | Value | Source |
|---|---|---|
| Cost | ... | ... |
| Duration | ... | ... |
| Benefits | ... | ... |

OUTSIDE VIEW (class statistics — Flyvbjerg):
| Dimension | Class median | Class P80 / realisation rate | Source |
|---|---|---|---|

GREEN BOOK OPTIMISM-BIAS UPLIFT APPLIED:
| Dimension | Uplift % | Rationale |
|---|---|---|

ADJUSTED FORECAST RANGE:
| Dimension | Low | Central | High | vs inside view |
|---|---|---|---|---|

LOAD-BEARING ASSUMPTIONS:
- ...

CALIBRATION VERDICT: [inside view optimistic / aligned / conservative] — [review] on funding recommendation
EVIDENCE GAPS: [...]

Worked example

Input: Platform rollout — inside view: $4M, 9 months, $6M annual benefits.

Expected output (excerpt):

REFERENCE CLASS: Mid-market SaaS core-system replacements (n=4) [model knowledge — verify]
OUTSIDE VIEW: median cost +28%, duration +35%, benefit realisation 62% at 12 months
GREEN BOOK OPTIMISM-BIAS UPLIFT APPLIED: cost +20%, duration +25%, benefits -30% vs plan
ADJUSTED FORECAST RANGE: cost $4.8–5.2M; duration 11–13 months; benefits $3.8–4.2M annual [review]

Quality checks before delivering

• [ ] Inside and outside views both present
• [ ] Reference class named with ≥1 comparable or gap flagged
• [ ] Green Book uplift % explicit per dimension
• [ ] No single-point defensible forecast without range
• [ ] Flyvbjerg outside-view and Green Book cited in methodology line

Propose profile update

When a stable convention surfaces during this run (thresholds, naming, tone, output format, or recurring corrections), propose a profile update: show the exact diff against ~/.claude/plugins/config/claude-for-strategy/consulting/CLAUDE.md (org-wide facts go to org-profile.md), ask for confirmation, and write only on yes. Only /consulting:practice-setup auto-applies a full profile write.

Outputs

Follows plugin CLAUDE.md § Outputs. Natural next: /transformation:business-case with adjusted inputs, /consulting:exec-memo for IC brief, or profile update for org calibration discount.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: daddia
• Source: daddia/claude-for-strategy
• License: MIT

Install and usage instructions live in the source repository linked above.