Metrics matter, but they should always be plural. Focus on the speedometer, ignore the gas gauge, and you’re sure to stop short of your destination. But while the plague of metric monomania can occasionally be an issue in business, it’s an even bigger problem within the social sector. After all, market discipline forces business leaders to weigh tradeoffs between costs and sales, or between product quality and service level speed. Multiple metrics help executives get the balance right, even as they scale.

By contrast, nonprofits too often receive (well-intended) guidance from stakeholders like funders and board members to disproportionately zero in on a single goal: serving the maximum number of beneficiaries. That’s a perfectly understandable impulse, of course. But it confuses scale with just one impact dimension, reach. “We have to recognize that a higher number does not necessarily indicate transformation,” says Lisha McCormick, CEO of Last Mile Health, which supports countries in building strong community health systems. “Higher reach alone does not equate to impact.”

This is a problem because excessively defining and valuing programs by the number of people they serve can give rise to unintended consequences. Nonprofit leaders can find themselves discussing how to serve more people through “lighter touch” models or debating ambiguous metrics like “reached” or “touched” to expand participant numbers (while fighting uneasiness about the potential adverse implications for program quality).

This is a slippery slope.

The right way to expand a nonprofit’s impact is to build programs on three pillars: breadth, depth, and durability. Scaling means advancing all three of these dimensions simultaneously. And while the specific metrics an organization uses will vary, some version of each of those elements must be measured and advanced together to stay on track.

Let’s start with the example I know best, Generation, a global employment nonprofit network that recruits, trains, and places adult learners into careers that would otherwise be inaccessible to them. At Generation, we define “breadth” as the number of learners who graduate from our programs—the most basic unit of impact—but we also use depth to capture the employment and income outcomes of those graduates within three months of program completion. Finally, we also track durability, or how well these outcomes persist over time: We follow the financial and personal well-being of our alumni for up to five years after they graduate by measuring their ability to cover daily financial needs while saving for the future and taking care of their mental and physical health.

Read the full article about scaling nonprofit impact by Mona Mourshed at Stanford Social Innovation Review.