Proportionality is one of the most important, and most frequently misunderstood, concepts in social value measurement. Put simply, it means matching the depth, rigour, and cost of your measurement approach to the scale of the activity, the significance of the decisions it will inform, and the resources available to carry it out.
A village hall reporting on a £5,000 grant should not be expected to produce the same level of analysis as a national government programme worth millions. Equally, a multi-million-pound infrastructure investment should not rely on rough estimates and anecdote alone.
Where does the principle come from?
Proportionality is not a new idea. It runs through every authoritative UK framework for public spending, evaluation, and impact measurement.
HM Treasury’s Green Book (updated February 2026) states that business cases should contain sufficient detail to support sound decision-making, but should not take up more time and resources than is necessary. The effort involved should correlate to the scale, cost, complexity, and risk of the proposal. This applies not only to major capital projects but to any assessment of social value in the public sector.
The Magenta Book, HM Treasury’s central guidance on evaluation, echoes this position. Not all interventions require the same depth of assessment, and the resources devoted to evaluation should reflect the scale and significance of what is being examined.
Social Value International’s Principles link proportionality explicitly to Principle 8: Be Responsive. This requires that the level of rigour applied to an analysis is appropriate for the decisions the account is designed to inform. The SVI Standards are intentionally flexible, designed to be applicable to activities of any scale, from a small community project to a national programme.
The Procurement Act 2023 and PPN 002 make proportionality a legal requirement in public procurement. Award criteria relating to social value must be a proportionate means of assessing tenders, having regard to the nature, complexity, and cost of the contract. The weighting allocated to social value should reflect the nature of the contract, not a one-size-fits-all formula. In practice, this means social value criteria should be framed specifically to the contract in question. A facilities management contract with a large workforce might reasonably prioritise local employment and fair work outcomes; a specialist IT contract might focus on digital skills or accessibility. Requiring every supplier to address every possible social value outcome regardless of relevance would be disproportionate and potentially challengeable. For more on how proportionality applies in a procurement context, see our article on the role of procurement in authentic social value delivery.
European Commission GECES guidance on social impact measurement takes the same approach. Outcomes and impacts should be quantified where proportionate, meaning where it can be done without cost that is excessive compared to the benefit of having the measurement. The standard is explicitly designed to work for organisations of all sizes.
Why proportionality matters
Getting proportionality wrong creates real problems in both directions.
Over-measurement burdens small organisations with data collection and report writing that consumes time and resources better spent on delivery. Staff capacity that could go towards services ends up absorbed by proxy selection and analysis. As the Stanford Social Innovation Review has noted, it is not sensible for a small organisation to invest scarce resources in apparently elaborate estimates of social value, not least because those estimates are liable to crumble under serious scrutiny.
Under-measurement, on the other hand, leaves decision-makers without the evidence they need to allocate resources effectively. Programmes may continue to receive funding despite poor outcomes, while more effective interventions go unsupported. In a procurement context, weak measurement means commissioners cannot meaningfully distinguish between suppliers who will genuinely deliver social value and those making aspirational claims. Under-measurement also exposes organisations to accusations of social washing.
It is also worth distinguishing proportionality from the related concept of materiality, since the two are sometimes conflated. Materiality asks whether a piece of information would affect a stakeholder’s decision: if omitting it would misrepresent the organisation’s activities, it is material and should be included. Proportionality governs how that information is gathered and presented. An outcome can be material without requiring the most rigorous and expensive form of measurement. The two concepts work in tandem: materiality determines what to include; proportionality determines how deeply to investigate it.
What proportionate measurement looks like in practice
Proportionality is best understood as a spectrum of rigour rather than a binary choice between measuring and not measuring.
At the lightest end, an organisation might articulate a simple Theory of Change, collect basic output data, and gather qualitative feedback through a short survey or informal conversations. This may be entirely sufficient for a small project seeking to demonstrate its value to a local funder, provided the approach is honest about its scope and limitations.
At an intermediate level, an organisation might use established financial proxies to monetise key outcomes, apply basic adjustments for deadweight, and produce a social value report using a platform such as the Social Value Engine. This gives commissioners and funders a credible figure that can be compared across different activities, without requiring specialist consultancy for every project.
At the most rigorous end, a full evaluative SROI analysis involves extensive primary stakeholder research, bespoke proxy development, detailed sensitivity analysis, and independent assurance. This level of investment is appropriate for major programmes where findings will inform significant resource allocation decisions, or where external credibility is paramount.
Every position on this spectrum can be valid. What matters is that the approach chosen is appropriate to the context, and that any limitations are openly acknowledged.
| Level | Approach | Appropriate for |
|---|---|---|
| Light | Theory of Change, output data, qualitative feedback | Small projects, local funders |
| Intermediate | Established proxies, monetised outcomes, platform-generated report | Commissioners, grant funders |
| Full | Primary stakeholder research, bespoke proxies, sensitivity analysis, independent assurance | Major programmes, significant resource decisions |
Key questions to guide your approach
What decisions will this evidence inform? This is the single most important question. A forecast SROI to help a board decide whether to launch a new programme requires different rigour from an evaluative SROI for a £50 million health intervention. Internal learning exercises need less formal verification than reports prepared for external funders or regulators.
What is the scale of the activity? A community garden project with a £3,000 annual budget does not need to apply deadweight, attribution, and displacement adjustments with the same precision as a national employment programme. It may be appropriate to use secondary research, existing proxy values, and a simplified Theory of Change rather than commissioning primary stakeholder research, as long as the approach still follows sound principles and is transparent about its limitations.
What resources are available? Government evaluation strategies suggest devoting around 1 to 10% of programme spend to evaluation. For smaller organisations the figure will be lower in absolute terms, but technology can help close the gap. Purpose-built platforms like the Social Value Engine can automate much of the analytical work, making proportionate measurement accessible to organisations that lack in-house evaluation expertise.
Who is your audience? An internal management report can rely on reasonable estimates with clearly stated assumptions. A report to external funders or investors will typically need more robust evidence, and may benefit from independent verification. Social Value International’s assurance framework offers three levels of scrutiny, from self-assessment through to full independent assurance, allowing organisations to select the level that fits their context.
Practical tips
- Start with the decision, not the methodology. Before choosing a measurement approach, clarify what question you are trying to answer and who needs the answer. This prevents both over- and under-investment in the process.
- Use existing data wherever possible. Many organisations already collect information that can serve social value measurement purposes: satisfaction surveys, employment records, attendance figures, referral data. Repurposing existing data is far more proportionate than designing bespoke collection instruments for every project.
- Be transparent about your approach and its limitations. A proportionate analysis that openly states its assumptions, the proxies used, and areas of uncertainty is more credible than an apparently rigorous one that obscures its methodology. Transparency is one of the eight Principles of Social Value for good reason.
- Build measurement in from the outset. Retrofitting evaluation after a project ends is always more expensive and less reliable than planning for it from the start. Even simple steps, like agreeing outcomes and indicators at the design stage, can dramatically improve the quality of evidence available later.
- Apply sensitivity analysis at every level. Even a light-touch analysis benefits from testing what happens to the results if key assumptions change. If an SROI ratio holds across a range of plausible scenarios, the findings are more robust regardless of overall rigour. If it is highly sensitive to one assumption, that signals where further investigation may be warranted.
- Do not let perfect be the enemy of good. Some measurement, done honestly and transparently, is almost always better than none. Organisations that wait until they can afford a full SROI analysis before doing anything risk never measuring at all.
Conclusion
Proportionality is not a concession to lower standards, but a principle of good practice embedded in every serious framework for social value measurement, from the Green Book to the Principles of Social Value, from the Procurement Act to the European Commission’s guidance on social impact.
Measure what matters, to the depth the situation requires, with the resources you have, and be honest about what you know and what you don’t. That is proportionate measurement, and it is how social value practice becomes genuinely useful rather than just a compliance exercise.
