RESULT OBTAINED
03 · Market size
Market size: build a defensible estimate
What must be established
A useful analysis leaves its controls visible.
- 01
Choose a unit suited to the decision: revenue, volume, accounts or use occasions.
- 02
Reconcile at least two independent estimation approaches.
- 03
Show the range, reference year and sensitive assumptions.
Decision checkpoint
Make the next choice explicit.
DECISION SUPPORTED
How can the value or volume of a market be estimated when the available data are incomplete?
DELIVERABLE TO RETAIN
A low, central and high estimate with calculation steps, sources, assumptions and a confidence assessment.
NEXT ITEM TO INVESTIGATE
Define the marketExplore →Choose the measure before collecting data
Revenue, unit volume, active accounts, installed base and usage occasions answer different questions. The estimate names its currency, price basis, tax treatment, period, geography and value-chain level before sources are combined. A conversion between units must expose the price or usage assumption that makes it possible.
- Decision unit
- Price basis
- Reference period
- Value-chain level
Build independent top-down and bottom-up paths
A top-down path starts with a documented broader population and applies stated filters. A bottom-up path combines observable units such as buyers, sites, volumes or transactions with stated rates. The paths are not averaged by default: their gaps identify a boundary, data or assumption that needs investigation.
- Top-down population
- Bottom-up drivers
- Explicit filters
- Reconciliation gap
Publish uncertainty as an operating condition
Low, central and high cases vary the inputs that actually move the result. The note identifies the source date, missing values, non-comparable definitions and the threshold at which the estimate would change the investment decision. This prevents a single attractive number from standing in for access or ability to win.
- Range
- Sensitive inputs
- Confidence
- Decision threshold
Application protocol
Turn the method into a reviewable decision record.
The page is complete only when another reviewer can reproduce the boundary, trace the evidence and understand what would change the conclusion.
Frame before measuring
Name the owner, decision, alternatives, unit, geography and horizon before collecting figures. This prevents a convenient source or familiar category from silently defining the problem.
- Decision and owner
- Comparable options
- Unit, boundary and horizon
Separate observation from judgement
Record every observation with source, date, method and unit. Keep transformation rules, scores and weights apart from the evidence so that disagreement can target the right layer.
- Observed evidence
- Calculation convention
- Assumption and confidence
Plan the reopening rule
State the signal, threshold, owner and review date that would reopen the choice. A robust conclusion is conditional and operational; it is not made permanent by a polished score.
- Material signal
- Decision threshold
- Owner and review date
Resources
Reuse the method and check its foundations.
- UK Government, The AQuA Book, 2025 (opens in a new tab)Official guidance on transparent assumptions, uncertainty, quality assurance and validation of analytical models.
- OECD, Competition Assessment Toolkit (opens in a new tab)Official toolkit useful for making market structure, regulatory conditions and assumptions visible when interpreting an estimate.
01Explicit scope
Unit, horizon and boundaries are visible.
02Qualified evidence
Source, date, method and confidence are recorded.
03Sensitivity tested
Weights and assumptions that reverse the result are known.
04Review planned
Signal, threshold, date and owner are named.
RETURN TO THE DECISION SYSTEM
See the canonical definition of marketing strategy→