Data & evidence

Estimation

Calculating emissions from a proxy rather than a measurement — using spend, industry averages, or modelled assumptions where actual data doesn't exist. Most Scope 3 disclosures rest substantially on estimation.

Corewell covered

What it is

Estimation is how almost every company starts. You can't measure what you don't have access to, and spend-based methods produce a number quickly from data you already hold. The problem appears later, in two forms. First, a spend-based estimate is a function of how much you bought, not how cleanly it was made — so switching to a lower-carbon supplier at the same price shows no improvement at all. Your disclosure becomes insensitive to the exact thing you're trying to change. Second, assurance treats estimated and measured data differently. An auditor can accept a well-documented estimate. They cannot accept an estimate presented as a measurement, and they can't accept either without knowing which one it is. The mature position isn't to eliminate estimation. It's to know precisely which figures are estimated, to say so in the disclosure, and to replace them where the category is material.

Why it matters

Estimated figures are legitimate and often unavoidable, but they behave differently from measured ones: they don't move when you reduce emissions, and they attract scrutiny under assurance. The risk isn't estimating — it's estimating without saying so.

How it connects

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