The Humane League is on quite a roll. Last fall, THL, an advocacy group that aims to reduce animal suffering, pressured foodservice giant Aramark to agree to improve its treatment of broiler chickens, a important victory as the animal welfare movement turns its attention to the chickens we eat, along with egg-laying hens. The nonprofit Animal Charity Evaluators again named THL one of its three top charities. Most important, the Open Philanthropy Project, a collaboration between GiveWell and Good Ventures, which is the family foundation of Dustin Moskovitz, the co-founder of Facebook, and his wife Cari Tuna, has in the last year given $3 million to The Humane League. Those donations are game-changers for an organization that just a couple of years ago had a budget of about $922,000.

The Humane League stands out because of its willingness, nay, eagerness to figure out what works when it comes to advocacy–not an easy task. A grass-roots organization with organizers based in 14 cities, THL has pivoted from one tactic to another, starting with broad public outreach around animal cruelty and vegan eating, then putting its activists and volunteers behind Meatless Monday campaigns in public schools and, most recently, focusing on corporate campaigns like the one against Aramark. There’s a lesson there for advocacy groups of all kinds–constantly ask yourself whether what you are doing is working.

“We’re very utilitarian,” says David Coman-Hidy, THL’s executive director. “We don’t want to get tied to any one tactic.”

As Animal Charity Evaluators wrote in its review of THL:

THL’s most significant advantage is not any single program, but rather its general approach to advocacy. Among animal advocacy organizations, THL makes exceptionally strong efforts to assess its own programs and to look for and test ways to improve them.

THL is just getting going. Its fledgling research arm, called Humane League Labs, is led by a committed volunteer named Harish Sethu, who is a Ph.D. computer scientist, university professor and former IBM executive who worked on the powerful computer Deep Blue. Sethu plans to conduct a rigorous study to see if animal advocacy actually changes what people eat–a fundamental question about which, surprisingly, little research has been done.

Then again, maybe it’s not that surprising. The impact of advocacy is hard to measure, whether we’re talking about animal welfare, climate change, LGBT or women’s issues, health care or tax policy. This is obviously a problem. Nonprofits spend lots of time and money on what looks to me like pointless advocacy. The Sierra Club declares that it is horrified by Scott Pruitt, the man nominated by Donald Trump to lead EPA. Teachers unions launch an aggressive campaign against Betsy DeVos, Trump’s choice for education secretary. Will these campaigns stop their nominations, or lead to greater support for the environment or public schools? It’s impossible to know, but I’m dubious. I’m fairly certain that advocacy groups don’t devote enough time and money to testing their tactics and their messages. What, for example, has been bought with the hundreds of millions of dollars poured into climate-change advocacy in the last decade? Where’s the climate movement, beyond the campuses? It certainly wasn’t evident on November 8.

To their credit, Coman-Hidy and Sethu are honest about what they don’t know. They don’t know, for instance, whether leaflets or online ads that are designed to persuade people to eat less meat — a longtime tactic of the animal welfare movement — have a lasting impact. “There are a lot of strong opinions,” Sethu told me. “But they have not been tested in a very rigorous fashion.”

Sethu hopes to change that by developing what amounts to a randomized controlled trial to see whether The Humane League’s advocacy is working. His plan is to identify zip codeswith similar demographics and political affiliations, roll out leaflets or targeted ads in one or more zip codes (the treatment group) and leave the rest alone (the control group). He would then purchase grocery store scanner data to see how the advocacy affected consumption of animal products. Most studies of animal-welfare advocacy rely on self-reported data, which is less reliable.

“It’s an ambitious project that requires a lot of preparatory work,” Sethu says. (To get the job done, Humane League Labs is hiring.) His intuition, he says, is that animal advocacy works: “We all became vegetarians or vegans because of advocacy of some kind. But we’d like to quantify it.”

Advocacy without impact

Interestingly, though, when Mercy for Animals, another animal welfare group, conducted a small study to see if online videos of farmed animal cruelty led people to change their eating habits, they found no meaningful impact.

Lewis Bollard, who leads the Open Philanthropy Project’s work on farm animal welfare, is among those who wonders whether vegan leaflets and online ads change behavior. As he wrote last year:

I haven’t seen compelling evidence that these interventions work; I know of few examples of social movements achieving widespread changes in personal behavior as deeply ingrained as eating habits.

[A quick aside: The uncertainty about behavior change inside the animal welfare movement has a parallel in the long-running conversation among environmentalists about whether so-called “conscious consumers” can help save the planet. The evidence suggests that they cannot.]

But as animal-welfare groups try, collectively, to figure out what works, at events such as the 2016 Symposium on Multidisciplinary Research in Effective Animal Advocacy at Princeton, Coman-Hidy faces a practical problem, albeit an exciting one: How to spend the infusion of money to the Humane League, and in particular the last Open Philanthropy grant of $1 million, which is unrestricted. (All the OpenPhil grants are for two years.)

He told me that he’s planning more corporate campaigns, not just in the US but also abroad, to capitalize on The Humane League’s ability to mobilize people. He’s confident, he says, that “aggressive campaigns play a big part in moving the ball forward.” THL is already operating on a small scale in the UK, and it helped start a global coalition against caged hens called the Open Wing Alliance.

The organization is also investing more in its staff, which numbers more than 50 people, and in its volunteers. Andrea Gunn, THL’s managing director, leads this work and, not surprisingly, it is evidence-based. THL periodically survey its employees, and recently distributed an anonymous survey in which workers rated their direct supervisors, in an effort to develop better managers. THL has also raised salaries–starting pay is now in the mid-to-upper $20,000 range–and improved health benefits.

This is smart. Because while we may not know much about which forms of advocacy work best, we can be sure organizations need to identify and develop skilled activists if they want to build broad and effective movements for change.