Thanks Chris, that's a cool idea. I will give it a go (in a few days, I have an EAG to recover from...)

One thing I should note is that other comments on this post are suggesting this is well known and applied, which doesn't knock the idea but would reduce the value of doing more promotion. Conversely, my super quick, low-N look into cash RCTs (in my reply below to David Reinstein) suggests it is not so common. Since the approach you suggest would partly involve listing a bunch of RCTs and their treatment/control sizes (so we can see whether they are cost-optimised), it could also serve as a nice check of just how often this adjustment is/isn't applied in RCTs

For bio, that's way outside of my field, I defer to Joshua's comment here on limited participant numbers, which makes sense. Though in a situation like early COVID vaccine trials, where perhaps you had limited treatment doses and potentially lots of willing volunteers, perhaps it would be more applicable? I guess pharma companies are heavily incentivised to optimise trial costs tho, if they don't do it there'll be a reason!

As a quick data point I just checked the 6 RCTs GiveDirectly list on their website. I figure cash is pretty expensive so it's the kind of intervention where this makes sense. 

It looks like most cash studies, certainly with just 1 treatment arm, aren't optimising for cost: 

Suggests either 1) there's some value in sharing this idea more or 2) there's a good reason these economists aren't making this adjustment. Someone on Twitter suggested "problems caused by unbalanced samples and heteroskedasticity" but that was beyond my poor epidemiologist's understanding and they didn't clarify further.

Hi Christian-- agreed but my argument here is really for fewer  treatment participants, not smaller treatment doses

Ah, that's helpful data. My experience in RCTs mostly comes from One Acre Fund, where we ran lots of RCTs internally on experimental programs, or just A/B tests, but that might not be very typical!

Hey Aidan-- that's a good point. I think it will probably apply to different extents for different cases, but probably not to all cases. Some scenarios I can imagine:

1. A charity uses its own funds to run an RCT of a program it already runs at scale: 
   • In this case, you are right that treatment is happening "anyway" and in a sense the $ saved in having a smaller treatment group will just end up being spent on more "treatment",  just not in the RCT. 
   • Even in this case I think the charity would prefer to fund its intervention in a non-RCT context: providing an intervention in an RCT context is inherently costlier than doing it under more normal circumstances, for example if you are delivering assets, your trucks have to drive past control villages to get to treatment ones, increasing delivery costs. 
   • That's pretty small though, I agree that otherwise the intervention is basically "already happening" and the effective savings are smaller than implied in my post
   • That said, if the charity has good reason to think their intervention works and so spending more on treatment is "good", the value of the RCT in the first place seems lower to me

• 2) A charity uses its own funds to run an RCT of a trial program it doesn't operate at scale:
  • In this case, the charity is running the RCT because it isn't sure the intervention is a good one
  • Reducing the RCT treatment group frees up funds for the charity to spend on the programs that it does know work, with overall higher EV
• 3) A donor wants to fund RCTs to generate more evidence: 
  • The donor is funding the RCT because they aren't sure the intervention works
  • Keeping RCT costs lower means they can fund more RCTs, or more proven interventions
• 4) A charity applies for donor funds for an RCT of a new program:
  • In this case, the cheaper study is more likely to get funded, so the larger control/smaller treatment is a better option for the charity

Overall, I think cases 2/3/4 benefit from the cheaper study. Scenario 1 seems more like what you have in mind and is a good point, I just think there will be enough scenarios where the cheaper trial is useful, and in those cases the charity might consider this treatment/control optimisation. 

Hi Nick-- thanks for the thoughtful post! 

I think cash arms make a lot of intuitive sense, my main pushback would be a practical one: cash and intervention X will likely have different impact timelines (e.g. psychotherapy takes a few months to work but delivers sustained benefits, perhaps cash has massive welfare benefits immediately but they diminish quickly over time). This makes the timing of your endline study super important, to the point that when you run the endline is really what determines which intervention comes out on top, rather than the actual differences in the interventions. I have a post on this here with a bit more detail.

Your point on the ethics here is an interesting one, I agree that medical ethics might suggest "control" groups should still receive some kind of intervention.  Part of the distinction could be that medical trials give sick patients placebos, which control patients accurately believe might be medicine, which feels perhaps deceptive, whereas control groups in development RCTs are well aware that they aren't receiving any intervention (i.e. they know they haven't received psychotherapy or cash), which feels more honest?

The downside is this changes the research question from "What is the impact of X?" to "How much better is X than cash", and there are lots of cases were the counterfactual really would be inaction. A way around this might be to give control groups an intervention that we know to be "good" but that doesn't affect the specific outcome of interest. e.g. I've worked on an agriculture RCT that gave control groups  water/sanitation products that had no plausible way to affect their maize yield but at least meant they weren't losing out. This might not apply to broad measures like WELBYs

I'm honestly not sure about the ethical side here though, interested to explore further. 

I really appreciated this short, clear post. Thank you!

Hey!

LEEP is indeed working on this -- I mentioned them in my original comment but I have no connection to them. I was thinking of a campaign on the $100M/year scale, comparable to Bloomberg's work on tobacco. That could definitely be  LEEP,  my sense (from quick Googling and based purely on the small size of their reported team) is they would have to grow a lot to take on that kind of funding, so there could also be a place for a large existing advocacy org pivoting to lead elimination. I have not at all thought through the implementation side of things here. 

How does the time and monetary cost of buying these products compare to the time and monetary cost of giving cash?

The total value of the bundle ($120) includes all staffing (modelled at scale with 100k recipients), including procurement staff, shipping, etc. This trial was a part of a very large nonprofit, which has very accurate costs for those kinds of things.

But obviously the researchers didn't know beforehand that the programs would fail. So this isn't an argument against cash benchmarking.

That's true, I don't think I made my point well/clearly with that paragraph. I was trying to say something like, "The Vox article points to how useful the cash comparison study had been, but the usefulness (learning that USAID shouldn't fund the program) wasn't actually due to the cash arm".  That wasn't really an important point and didn't add much to the post. 

I really like the idea of asking people what assets they would like. We did do a version of this to determine what products to offer, using qualitative interviews where people ranked ~30 products in order of preference. This caused us to add more chickens and only offer maize inputs to people who already grew maize. But participants had to choose from a narrow list of products (those with RCT evidence that we could procure), I'd love have given them freedom to suggest anything. 

We did also consider letting households determine which products they received within a fixed budget (rather than every household getting the same thing) but the logistics got too difficult. Interestingly, people had zero interest in deworming pills, oral hydration salts or Vitamin A supplements as they not were aware of needing them-- I could see tensions arising between households not valuing these kinds of products and donors wanting to give them based on cost-effectiveness models. This "what do you want" approach might work best with products that recipients already have reasonably accurate mental models of, or that can be easily and accurately explained.

At a very basic intuitive level, hearing "participants indicated strong preference for receiving our assets to receiving twice as much cash" feels more persuasive than comparing some measured outcome between the two groups (at least for this kind of asset transfer program where it seems reasonable to defer to participants about what they need/want)

Very interesting suggestion: we did try something like this but didn't consider it as an outcome measure and so didn't put proper thought/resources into it. We asked people, "How much would you be willing to pay for product X?", with the goal of saying something like "Participants valued our $120 bundle at $200" but unfortunately the question generally caused confusion: participants would think we were asking them to pay for the product they'd received for free and either understandably got upset or just tried lowballing us with their answer, expecting it to be a negotiation. 

If we had thought of it in advance, perhaps this would have worked as a way to generate real value estimates:

• We randomise participants into groups
• The first group is offered either our bundle (worth $120) or $120 cash
• If >50% take the bundle, we then adjust our cash offer upwards and offer it to another group (or the opposite if <50% take the bundle)
• We repeat this process of adjusting our price offer until we have ~50% of participants accepting our cash offer: that equilibrium price is then the "value" of the bundle
• I'm not sure what the sample size implications would be but a big advantage would be the timeline: this could be done in a few weeks, not years
• I bet proper economists have a way to do this but it's interesting to brainstorm on

I can see a few issues with this:

• We still have to assume people "know what's best for them": that's a really patronising statement, but as above, people need reliable mental models to make these decisions, and won't have that for novel products
• We need to have donors who will accept this measure: the data only really matters when it informs decisions

I'm very open to other thoughts here, I really like the concept of a cash benchmark and would love to find a way to resurrect the idea.