Impact Measurement Frameworks: IRIS+, IMP, and Beyond
What Frameworks Are Used to Measure Impact?
Impact measurement is the most technically demanding aspect of impact investing. Unlike financial returns — which have standardized definitions and universal methodologies — impact outcomes vary enormously by sector, geography, beneficiary, and theory of change. Investors in clean energy, microfinance, affordable housing, healthcare, and education are measuring fundamentally different things. Several frameworks have emerged to standardize approaches: IRIS+ provides standardized metric definitions; the Impact Management Project provides a conceptual classification framework; GIIRS provides fund-level impact ratings; and SDG mapping connects investments to international development goals. Understanding which frameworks apply to which use cases is essential for evaluating impact fund quality.
Impact measurement frameworks provide standardized methodologies for defining, collecting, and reporting impact metrics — enabling comparison across investments, accountability to stakeholders, and improvement of impact practice over time.
Key Takeaways
- IRIS+ (Impact Reporting and Investment Standards) is the GIIN's catalog of standardized metric definitions, used to ensure comparable measurement across impact investments.
- The Impact Management Project (IMP) provides a five-dimension classification framework (What, Who, How Much, Contribution, Risk) that structures how impact is described and assessed.
- GIIRS (Global Impact Investing Rating System, now B Analytics/GIIN data) provides fund-level impact ratings that allow institutional investor comparison.
- SDG mapping connects investments to UN Sustainable Development Goals, providing high-level impact narrative and enabling portfolio SDG contribution reporting.
- No single framework dominates — sophisticated impact investors use multiple frameworks in combination, choosing elements appropriate for their specific strategies.
IRIS+ (Impact Reporting and Investment Standards)
IRIS+ is maintained by the GIIN as a free, publicly available catalog of standardized impact metrics. As of 2024, it contains over 1,000 defined performance indicators organized into:
Theme-based metric sets: Curated metric sets for 25 impact themes (agricultural production, affordable housing, clean energy, education, financial services, healthcare, water and sanitation, etc.). Each theme set identifies the most important metrics for measuring impact in that sector.
Standardized metric definitions: Each IRIS+ metric has a precise definition specifying what is measured, how it is calculated, and what is included/excluded. For example, "PI5533 — Employees: Median Wage" has a specific definition ensuring comparability across organizations.
SDG alignment: IRIS+ metrics are mapped to relevant UN SDGs, enabling investors to connect metric collection to SDG contribution claims.
Usage guidance: IRIS+ provides guidance on which metrics to prioritize, how to collect data, and what verification approaches are appropriate.
How IRIS+ Is Used in Practice
Impact investors use IRIS+ by:
- Selecting a theme-based metric set aligned with their investment thesis
- Identifying a subset of core metrics from that set as mandatory reporting for investees
- Defining data collection processes and timelines
- Aggregating reported metrics across portfolio investments for portfolio-level impact reporting
IRIS+ adoption is widespread among institutional impact investors and required by many development finance institutions for their private equity and private debt co-investors.
The Impact Management Project (IMP)
The IMP is a collaborative initiative involving hundreds of leading organizations in impact investing. Its primary contribution is the five-dimension framework for classifying and assessing impact:
Dimension 1: What
What outcomes does the enterprise contribute to? What is the importance of those outcomes to people and the planet?
- Identifies the social/environmental outcome (health improvement, CO₂ reduction, income increase)
- Assesses the baseline severity of the problem in the absence of the activity (deep-poverty contexts produce more impact from income increases than already-affluent contexts)
Dimension 2: Who
Who experiences the outcomes? How underserved are the beneficiaries relative to others?
- Characterizes the target population (specific geography, income level, demographic)
- Assesses depth of deprivation — outcomes affecting the most underserved have greater impact value
Dimension 3: How Much
How many people experience the outcomes, and to what degree?
- Scale: number of beneficiaries
- Depth: magnitude of change per beneficiary
- Duration: how long the change persists
Dimension 4: Contribution
How significant is the enterprise's contribution to the outcome? What is the counterfactual?
- Assesses additionality: would outcomes have occurred without this enterprise?
- Distinguishes "significant" (outcome requires this actor) from "marginal" (outcome likely without this actor)
Dimension 5: Risk
What is the risk that outcomes differ from expectations?
- Impact risk: risk that outcomes are not achieved as predicted
- Stakeholder risk: risk that stakeholders, not the investor, define whether impact occurred
- Drop-off risk: risk that outcomes do not persist after the intervention ends
The IMP framework produces structured impact descriptions that are comparable across investments — enabling investors to communicate clearly about impact quality, not just impact quantity.
GIIRS and B Analytics
GIIRS (Global Impact Investing Rating System) is a fund-level impact rating system originally developed by B Lab and now managed through GIIN's data infrastructure. GIIRS assesses the impact practices of impact funds and companies on a star-rated basis:
Fund-level assessment: Impact strategy, governance, engagement approach, and portfolio impact management.
Company-level assessment: Impact on workers, community, environment, customers, and governance.
GIIRS ratings allow institutional investors to compare impact funds on a standardized basis — the fund analogue to GRESB for real estate or GIIRS for impact funds.
SDG Mapping
The UN Sustainable Development Goals (SDGs, 2015–2030) provide a widely recognized framework for classifying impact by global development priority. Many impact investors map their portfolios to SDGs as a communication tool:
Revenue alignment: What percentage of portfolio revenue comes from activities aligned to each SDG?
Outcome contribution: Which SDG targets do the fund's outcomes contribute to?
SDG priority: Some investors prioritize specific underinvested SDGs (SDG 10 Reduced Inequalities, SDG 13 Climate Action, SDG 3 Good Health) in fund design.
SDG mapping is widely adopted but has limitations: SDG alignment is a narrative tool rather than a measurement methodology. Revenue exposure to an SDG-aligned sector is not equivalent to measured progress toward SDG targets.
Choosing the Right Measurement Framework
No single framework is universally appropriate. Selection depends on:
Investment stage and scale:
- Seed/early-stage: Simple output metrics + IMP dimension assessment
- Growth stage: Full IRIS+ metric set + IMP + verification
- Portfolio/fund level: GIIRS + SDG mapping + PCAF for climate
Sector:
- Financial services: IRIS+ financial services theme + microfinance-specific PAI metrics
- Energy: IRIS+ clean energy theme + CO₂ avoidance calculation
- Housing: IRIS+ affordable housing theme + location-specific affordability analysis
Reporting obligation:
- SFDR Article 9: PAI indicators (specific regulatory requirement)
- DFI co-investors: Often require IRIS+ metric sets
- Institutional LP expectations: GIIRS rating + IMP framework description
Common Mistakes
Reporting outputs as impact. "We disbursed 50,000 loans" is an output metric, not an impact metric. An impact metric would be "50,000 borrowers increased household income by an average of 22%." IRIS+ provides both output and outcome metrics — selecting only output metrics is insufficient for impact claims.
Mapping to SDGs without outcome measurement. Claiming SDG 7 (Clean Energy) impact because the portfolio includes renewable energy companies is SDG alignment, not SDG impact measurement. Impact measurement requires outcome data, not sector membership.
Using non-standardized metrics. Inventing proprietary metrics that cannot be compared to other impact investors reduces credibility and prevents benchmarking. IRIS+ exists specifically to avoid this — use standardized definitions wherever available.
Related Concepts
Summary
IRIS+ provides standardized metric definitions that enable comparable impact measurement across investments; the IMP five-dimension framework provides structured classification of impact quality; GIIRS provides fund-level impact ratings for institutional comparison; and SDG mapping connects investments to international development goals. No single framework is universally appropriate — selection depends on investment stage, sector, and reporting obligation. The most important distinction in any framework application: output metrics (what was delivered) versus outcome metrics (how lives changed). Credible impact reporting requires outcome measurement, not just output tracking.