Campaign donations always carry the whiff of something unsavory, but, aside from cases of straightforward, Tammany Hall-style vote buying, it can be hard to follow the money and untangle influence peddling. Two political science graduate students have taken a crack at measuring what political contributions buy, using the same randomization protocols that doctors would use in a medical trial to try to measure the effect that money had on a target.

David Broockman and Joshua Kalla, of UC Berkeley and Yale University respectively, partnered with CREDO Action, a left-leaning advocacy group to conduct their measurements in the midst of a real-world lobbying push. In this experiment, CREDO had affiliated donors request meetings with 191 Congressional offices, but only mentioned their history of donations in a random third of the initial requests. The meeting requests were identical, except for referring to the senders as either “local constituents” or “local campaign donors.”

The advocates were five times more likely to meet with either the Congressperson him or herself or the Chief of Staff when the initial request mentioned donations. There was no discussion of explicit quid pro quo dealings in the message or at the meeting, but prior donations had, in essence, bought access to senior, decision-making staff. The researchers hypothesize that donations might be even more powerful in lobbying than they measured, since lobbyists may make more explicit promises or reveal the sums previously donated, though the researchers did not.

The researchers stated that their goal was to make the discussion of money in politics slightly less speculative and to better inform judges who may face cases like Citizens United. Their findings suggest that money augments speech, so that contributors have more opportunities to meet and try to persuade the beneficiaries of their largess.

Access-buying may be most important to resolve intra-party tensions, rather buying victory for a partisan issue. A reasonably high proportion of lobbying is not aimed at flipping votes on an issue, but in persuading ideological allies to move an issue up their list of priorities and to expend political capital in cosponsoring a bill or holding a press conference. So, in these cases, Democratic firms like CREDO might not be competing for influence with opponents on the right, but with other left-leaning firms that prioritize legislation differently.

Just as empirical research into get out the vote and fundraising methods has expanded over the last decade, Broockman and Kalla’s research is likely not to be the last field test of its kind. It’s easy to imagine their experiment repeated with explicit references to donation amounts, allowing them to approximate a dose-response curve, applying the same statistics that doctors use to determine the optimal use of a drug to choose the ideal amount of money to give.

If this research drives big shifts in our opinions of political contributions, that change probably won’t be driven by the academic papers themselves, but by the way conventional lobbying firms and new political players tout their results.

GiveWell, one of the leading firms in the effective altruism movement, has been exploring the possibility of adding political advocacy to their list of recommended giving opportunities. GiveWell takes a utilitarian approach to charity, auditing their recommended causes not just for the percent of their funds spent on salaries and overhead, but for the measurable impact each marginal dollar for the cause can buy. If GiveWell were to recommend political advocacy, it would be because their researchers had been able to assess the projected impact of money on a policy issue near a tipping point, and rated it a good buy.

When charity firms can set up thermometer style fundraising drives, promising donors that if they can close the gap, a charter school bill will be passed, Americans may wind up with a sour taste in their mouths. It’s true that, at present, advocacy groups make similar pitches (“Donate NOW to Block Bill X”), but voters may find the implicit costs of purchasing influence more aesthetically acceptable than explicit models and pricing.

Hard numbers may prove more persuasive than anecdotes about Washington’s pay-to-play culture, but citizens should be mindful of measurement bias. It was easier to measure earmarks than to anticipate the gridlock that would result from their ouster. The public funding for elections in Arizona, intended to curb corruption, has been alleged to stoke extremism, since, once candidates raise $5 each from 300 people, they’re given enough money to run a competitive campaign.

Political science can clarify the choices and tradeoffs we face, when we try to limit the influence of money and politics, but political philosophy is what should guide our final decisions.