Cost-effectiveness of Veganuary and School Plates

By Vasco Grilo🔸 @ 2025-02-28T17:31 (+23)

The views expressed here are my own, not those of people who provided feedback on the draft. I started this cost-effectiveness analysis in the context of Ambitious Impact’s (AIM’s) research program from September to December of 2024.

Summary

Cost-effectiveness

Veganuary

Veganuary is “a non-profit organisation that encourages people worldwide to try vegan for January and beyond”. I estimate Veganuary in 2024 averted 0.944 suffering-adjusted days (SADs) per $. I get this from the ratio between:

I calculate the benefits of Veganuary in 2024 multiplying:

School Plates

School Plates is a program from ProVeg UK aiming to increase the consumption of plant-based foods at schools and universities in the UK. I estimate School Plates in 2023 averted 15.3 SADs/$ multiplying:

Cage-free campaigns

I estimate cage-free corporate campaigns helping hens avert 78.8 SADs per $. I get this multiplying:

Comparisons

I estimate the cost-effectiveness of:

Discussion

Veganuary

According to Veganuary’s 6 month survey in 2024, 81 % of people decreased their consumption of animal products over the last 6 months by at least 50 %. In contrast, my assumptions imply a reduction in the meat supply per person over the 1st half of 2024 of 0.525 % (= (1 + 1 - 6/12)/2*0.007), which is less than 1.05 % (= 0.00525/0.5) of the reduction reported by 81 % of the people surveyed by Veganuary. I do not trust their survey’s data due to:

I would also add a question to the survey used to determine the number of people who participated in Veganuary which would check whether the respondents are replying in good faith. This is important because only a small fraction of the population participates in Veganuary, such that small errors matter.

I encourage Veganuary to include questions about the impact of their campaigns on the consumption of red meat, white meat, eggs, shrimp, and fish in the surveys they use to determine the number of people who reported participating in Veganuary.

I advise Veganuary to strongly emphasise that eating red meat and dairy products is much better for animals than eggs, white meat, fish, or other seafood. They can even experiment with alternative pledges like Beefuary, Reduary, Cheesuary, Milkuary, Dairyuary, Cattleuary, and Ruminanuary, where beef, red meat, cheese, milk, dairy products, cattle-, and ruminant-based foods are allowed[4]. One Step for Animals asks people to stop eating chicken. A pledge for flexitarians, Flexuary, may work too, but I think it would have to be made concrete, such as by asking people to only eat plant-based foods 4 days per week.

Wendy Matthews, international head of partnerships and expansion at Veganuary, thinks I greatly underestimated the impact of Veganuary by guessing total benefits to be 2 times as large as those linked to the people who reported participating in Veganuary. It would be great if they could quantitatively justify why the vast majority of their benefits come from influencing people who did not participate in Veganuary.

Vicky Cox, senior animal welfare researcher at AIM, also did a cost-effectiveness analysis of Veganuary. Vicky’s 6 estimates range from 0.722 to 97.3 SADs averted per $, i.e. 0.00916 (= 0.722/78.8) to 1.23 (= 97.3/78.8) times my estimate for cage-free campaigns. The highest estimate is 103 (= 97.3/0.944) times my estimate for the cost-effectiveness of Veganuary in 2024. In my model, it would correspond to assuming an effect size in terms of Glass’s Delta for January 2024 of 0.721 (= 0.007*103). I see this as unreasonably high even for a treatment group with just hundreds of people, so I do not think it is at all applicable to the 25 M people who reported participating in Veganuary in 2024. It is 6.01 (= 0.721/0.12) times the upper bound of the 95 % confidence interval of the meta-analytic effect size of Green et al. (2024).

School Plates

I estimate School Plates replaced 19.0 (= 64.5/3.4) times as many meals per $ in 2023 as Sinergia Animal’s analogous program, Nourishing Tomorrow. The cost-effectiveness of School Plates is proportional to the number of replaced lunches/dinners provided by Colette, but I have not checked how it was estimated, and organisations often inflate their impact. I asked Colette about it on February 13, but I have not heard back. I recommend School Plates to be transparent about how they estimate the number of meals they replace, and investigate their composition.

Comparisons

My estimate that School Plates in 2023 was 16.2 times as cost-effective as Veganuary in 2024 may be surprising. It implies a significant difference in their cost-effectiveness despite both focussing on decreasing the consumption of animal-based foods. I would not be surprised if the difference was smaller. Nevertheless, the difference is not large enough to raise red flags for me. The cost-effectiveness of human welfare interventions can vary much more than that. In the context of animal welfare, I estimate:

My results suggest cage-free campaigns are way more cost-effective than Veganuary, and more cost-effective than School Plates. Nonetheless, as illustrated above, I believe such campaigns are far from the most cost-effective intervention. I recommend people funding Veganuary, School Plates, and cage-free campaigns support the Arthropoda Foundation, SWP, or WAI.

My estimates for SADs averted rely on AIM’s pain intensities, which I believe greatly underestimate the intensity of excruciating pain. They say this is only 56.7 times as intense as hurtful pain, and I guess this is as intense as fully healthy life. So I infer AIM’s pain intensities imply excruciating pain is only 56.7 times as intense as fully healthy life. In this case, 1 day of fully healthy life plus 25.4 min (= 24*60/56.7) of “scalding and severe burning events [in large parts of the body]”, or “dismemberment, or extreme torture” would be neutral, whereas I believe it would be clearly bad. Yet, I do not think AIM’s much lower intensity of excruciating impacts much the comparisons between Veganuary, School Plates, and cage-free campaigns, as none of these overwhelmingly focuses on decreasing excruciating pain. Feel free to ask Vicky for the sheet with AIM’s pain intensities, and the doc with my suggestions for improvement.

Acknowledgements

Thanks to Sagar Shah, Vicky Cox, and Wendy Matthews for feedback on the draft[5].

  1. ^

     In this case, “variance of the monthly consumption of meat” = (“variance of the daily consumption of processed meat” + “variance of the daily consumption of non-processed red meat” + “variance of the daily consumption of non-processed poultry”)*“number of days per month”.

  2. ^

     “In this population, mean (standard deviation) consumption was 35.0 (34.0) g/day for processed meat, 31.9 (28.2) g/day for red meat, and 33.8 (28.3) g/day for poultry. The correlations between the intake of the different meat categories (in g/day) were: r = 0.05, p < 0.01 (between processed meat and red meat), r = -0.02, p = 0.21 (between processed meat and poultry), and r = 0.11, p < 0.01 (between red meat and poultry).”

  3. ^

     “Mean monthly consumption of meat” = (“mean daily consumption of processed meat” + “mean daily consumption of non-processed red meat” + “mean daily consumption of non-processed poultry”)*“number of days per month”.

  4. ^

     Thanks to ChatGPT for suggesting arguably catchy names.

  5. ^

     I listed the names alphabetically.

Toni Vernelli @ 2025-02-28T19:48 (+39)

We are grateful to Vasco for sharing this analysis with us prior to publication, for delaying in order to give us time to respond, and also for using his time to quantitatively explore the most impactful way to help animals. 

While we appreciate Vasco’s intentions in producing this analysis, we believe there are reasons to be much more optimistic about Veganuary’s impact. We feel Vasco’s results reflect arbitrary assumptions based on his priors, rather than high-quality evidence about our campaign’s effectiveness.

Vasco’s calculations imply that Veganuary counterfactually reduced meat consumption by an extraordinarily small amount – the equivalent of just 1.3K metric tonnes.  Around half of this is assumed to come from 25M direct pledge participants – who he assumes counterfactually reduce lifetime meat consumption by the equivalent of just 25g each (around 0.03% of annual meat consumption in the UK in 2021).  The other half comes from all Veganuary’s other work, including our corporate engagement work, which we believe reaches many more people.

We regrettably think Vasco made very big adjustments that reflect his pessimism about our impact, but neither the magnitude of these judgements nor the degree of underlying uncertainty is communicated very clearly in his post. For example, Vasco arbitrarily assumed that Veganuary’s impact on pledge participants is 10x lower than the average effect size from the Green et al (2024) meta-analysis. Vasco’s justification of this is that our spend per pledge participant (c.$0.13) is probably a lot lower than the interventions in the Green et al (2024) meta-analysis. 

We believe Veganuary might be a victim of its own success here.  Being able to reach millions of people at low cost by creatively leveraging media and inspiring improved retail and food service offerings is a potential signal of effectiveness – but Vasco appears to have used this as a negative signal about our impact.

Vasco also assumed that the counterfactual impact of our non-pledge work is about the same as our work to inspire pledge participation.  While this is hard to know for sure, we believe the counterfactual impact of our corporate engagement work to inspire more, better, and highly visible plant-based offerings in retailers and food service could be several times higher than arising from pledge participants.

We accept that properly measuring the counterfactual impact of interventions on animal product consumption is exceptionally hard, even more so with campaigns like Veganuary that gain national media coverage and influence product offerings at major retailers and food service outlets. We’d love to be able to allocate more resources towards measuring our impact.  We aren’t yet in a position to provide quantitative estimates we feel we can stand by, but the following results make us optimistic our impact is likely to be much higher than what Vasco set out in his analysis:

While we are grateful for Vasco’s commitment to seeking the most cost-effective way to help animals, we think he has made arbitrary judgements that make Veganuary look considerably less cost-effective than we believe it is and has not clearly explained these judgements in a way is helpful for readers. 

While we accept it is exceptionally difficult to measure the impact of interventions like Veganuary, which use the diet change element of its work to drive progress through corporate engagement, we welcome ideas from readers on ideas of how we might be able to do this (and resources to help run such studies).  We also welcome serious attempts to measure our effectiveness that legibly explain key cruxes/judgements/uncertainties, and credible suggestions on how we can improve our effectiveness (acknowledging we operate under constraints given our name, branding, and supporter base).   

Toni Vernelli, International Head of Communications, Veganuary

Vasco Grilo🔸 @ 2025-03-01T09:16 (+12)

Thanks, Toni!

Vasco’s calculations imply that Veganuary counterfactually reduced meat consumption by an extraordinarily small amount – the equivalent of just 1.3K metric tonnes.  Around half of this is assumed to come from 25M direct pledge participants – who he assumes counterfactually reduce lifetime meat consumption by the equivalent of just 25g each (around 0.03% of annual meat consumption in the UK in 2021).  The other half comes from all Veganuary’s other work, including our corporate engagement work, which we believe reaches many more people.

I agree these numbers follow from my assumptions, but they do not seem super low to me. I do not have strong expectations about the mean reduction in meat consumption in kg among the people who reported participating in Veganuary. Note "My effect size refers to people who reported participating in Veganuary. The number of people who actually participated may be significantly smaller. Veganuary concluded 25 M participated multiplying small fractions of participants in the surveyed countries by their populations. However, such fractions may be significantly explained by a few people mistakenly reporting their participation due to lack of attention or social desirability bias".

We regrettably think Vasco made very big adjustments that reflect his pessimism about our impact, but neither the magnitude of these judgements nor the degree of underlying uncertainty is communicated very clearly in his post. For example, Vasco arbitrarily assumed that Veganuary’s impact on pledge participants is 10x lower than the average effect size from the Green et al (2024) meta-analysis. Vasco’s justification of this is that our spend per pledge participant (c.$0.13) is probably a lot lower than the interventions in the Green et al (2024) meta-analysis. 

Nitpick. Using "For example" may suggest you think there are many other important assumptions I made which you think are "arbitrary". However, I guess my assumptions about the effect per person who reported participating in the pledge, and the effect on people who did not participate in the pledge, which you mentioned in your comment, are the most important, and the ones you disagree with the most. Are there others? If not, I think "Crucially" or "In particular" would communicate your views more faithfully than "For example".

We believe Veganuary might be a victim of its own success here.  Being able to reach millions of people at low cost by creatively leveraging media and inspiring improved retail and food service offerings is a potential signal of effectiveness – but Vasco appears to have used this as a negative signal about our impact.

My prior is that the effect per person decreases with the number of people affected. So more people being affected updates me towards a smaller effect per person. However, it does not necessarily update me towards a lower impact.

  • Meat reduction data from Germany’s Statistical Office: The German Federal Statistical Office (Destatis) published that based on scanner data from German food retailers, 29.4% less meat was purchased in January 2024 than in December 2023. Compared to the 2023 annual average, meat sales in January 2024 were 12.5% lower than the previous 12 months. Compared to the 2022 annual average, meat sales in January 2023 were 14.3% lower than the previous 12 months.

I do not know whether that was caused by Veganuary. The meat consumption per capita excluding fish and seafood in Germany peaked in 1987, well before Veganuary started in the UK in 2014, and has trended downwards unevenly since then.

From the point of view of animal welfare, it is much more important to look into the number of poultry birds and aquatic animals per capita. In Germany, the number of poultry birds per capita increased from 1.67 (= 135*10^6/(81.0*10^6)) in 2014 (when Veganuary started in the UK) to 2.07 (= 173*10^6/(83.6*10^6)) in 2020 (the last year for which there is data about the number of poultry birds on Our World in Data (OWID)), i.e. 24.0 % (= 2.07/1.67 - 1). The vast majority of this increased happened from 2014 to 2016.

  • New Research from the University of Exeter suggests that taking part in Veganuary leads to sustained reductions in meat consumption and can also produce fundamental shifts in people’s attitudes towards meat and their own self-identity as a meat-eater. Full study here.

The study looked into just 40 highly selected people[1], and there was no control group or measures to mitigate social desirability bias.

  • Kantar data from the UK shows that, for 832K people who gave up animal products for the first time in January 2019, sustained reductions in animal product purchases over the following six months totalled 4,452,603 kg – equivalent to sparing 3.6 million animals by our calculations.  While Veganuary cannot take all the counterfactual credit for these diet changes, it is striking how the estimated aggregate reduction in animal product consumption from pledge participants in just one country in 2019 is considerably higher than Vasco’s assumptions.

Could you share a link? I would not be surprised if only 1 % of that meat reduction had been caused by Veganuary, in which case there would be little tension with my results. I would also like to know about the changes in the consumption of specific types of animal-based foods.

  • I worry about replacements of red meat with white meat, eggs, and farmed aquatic animals, which respect a greater suffering per kg. Veganuary started in the United Kingdom in 2014, and the production of broilers per person in there in January increased 4.27 times as fast from 2014 to 2024 as from 1994 to 2013. Data about consumption (production plus net imports) would be more informative, and the production of broilers per person could have increased faster without Veganuary, but the correlation is still concerning.

While we are grateful for Vasco’s commitment to seeking the most cost-effective way to help animals, we think he has made arbitrary judgements that make Veganuary look considerably less cost-effective than we believe it is and has not clearly explained these judgements in a way is helpful for readers. 

I estimated Veganuary in 2024 was 1.20 % as cost-effective as cage-free campaigns, and that these are 0.718 % as cost-effective as SWP. So I think more optimistic assumptions about Veganuary would still leave it much less cost-effective that SWP.

  1. ^

    The pre-screen survey was completed by 1,125 people on Prolific. Of those, 60 were eligible participants (who were either omnivores or flexitarians and intended to take part in Veganuary or a different meat-free January challenge) and were invited to the baseline survey. 48 participants completed this survey without failing more than one of three attention check questions. All of these were invited to the follow-up survey in February which was completed without more than one failed attention check by all of the 40 people who participated in it.

PreciousPig @ 2025-03-03T19:40 (+18)

Dear Vasco,
Dear Team of Veganuary,

I want to thank you both for your input/contributions here as I think it is incredibly important to properly verify the actual effectiveness of any possible intervention to help animals. I have followed Veganuary’s success for many year and am a long-time donor, and have previously tried to estimate your actual impact, for example here.

 



Reasons I am positive about the impact of Veganuary:

I think there are some incredibly promising metrics about Veganuary’s success, for examnple this 2019 survey on why people go Vegan in which 12800 people participated, out of them 369 (a little under 3%) said that Veganuary was the first thing that seriously made them consider going Vegan. If we assume this metric is accurate and still holds true today, and that roughly 1% of the people in Europe and North America are Vegan (or very roughly 10 milllion people out of 1 billion people), as many as 280 000 people might be Vegan today because of Veganuary. If we further assume each Vegan person saves on average one animal’s live a day, that would be 100 000 000 (100 million) animals spared each year due to Veganuary. 
(I know I am making a lot of big assumptions here and some of those number are almost certainly too optimistic, for example an online poll like the one I linked will almost certainly overrepresent a primarily online campaign like Veganaury. I also don’t know how to convert that number to the metric of SAD’s used here)

 



Reasons I think Veganuary might be less impactful than it used to be:

I also think there are some worrying signs about the success of Veganuary, specifically in the last three years.

1) My biggest reason for this is that the actual search interest in Veganuary is decreasing since 2022, google trends show that there there was only 57% as much search interest in Veganaury in January 2025 as there was in 2020 and 2022 (The two years with the highest search interest):
 



2) My second reason is that the amount of people who sign up to the core of your Veganaury Campaing – the 31 daily Emails – seems to be decreasing:

2022 Here is Veganaury’s 2022 report: https://veganuary.com/wp-content/uploads/2022/03/Veganuary-2022-End-Of-Campaign-Report.pdf where you reported 629 000 people signing up / 19,6 million emails sent (31,16 Emails per signup, so checks out pretty closely with 31 days in January)

2024 Heres the 2024 report: 
https://veganuary.com/wp-content/uploads/2024/03/Campaign-Report-2024-UK.pdf in which you no longer posted a direct amount of people who had signed up by Email, but you sent 17,5 million Emails. Assuming again 31,16 Emails per participant, that is around 560000 signups, a clear decrease from the 700k you reported in 2023. (https://veganuary.com/wp-content/uploads/2023/12/Veganuary-2023-EoC-Report-UK.pdf) – If I am correct here, last year was the first time your campaign significantly decreased compared to the year before in the amount of Email signups. I hope you will once again share the number of Email signups for Veganaury 2025 so we have a better comparison. 

I know you say your campaign has spread to other channels instead of just Email like YouTube, podcasts, etc. - But every single Veganuary website (All individual country campaigns) I visit still asks me only to sign up by Email, so I strongly believe that this is still the core of your campaign and the best indicator of your campaigns actual success. I also believe if your campaign in 2025 was much bigger than 2022 due to people using many other channels compared to just Email, we would see search interest increasing on Google trends instead of decreasing.
 


Suggestions how I think you can better verify your actual impact:

Besides continuing to share the number of Email signups, here are some ways how I think you could increase / confirm the accuracy of the YouGov survey:

1 – Run a similar YouGov Survey about a completely made up campaign similar to Veganaury and see if results are different. For example ask participants if they have participated in „Plantober“ – A challenge for people to eat plant based for the month of October – which does of course not exist, so we would expect that 0% respond that they participated in such a poll if it is accurate. If the number is above 0 but below the YouGov numbers for Veganuary, that might be a good indicator to how much the YouGov survey overestimates participation. If the results are similar to the YouGov poll about Veganaury, we should probably not trust these polls at all anymore. 

2 – Make the poll have 2 parts and do not direcly bring up Veganuary in it. For example:
Question 1 – Have you decreased your consumption of any specific type of product in the month of January?
Question 2 – Asked to anyone who answers „animal products“ / „meat“ or similar in question 1 – What was your primary motivation to do so? And then report the amount of people who say they decreased animal product consumption because of Veganuary. 
This would not only reduce social desirability as a factor since people would have to say what they reduced themselves, but also show what percentage of people who say they did decrease their animal product consumption did so because of Veganuary.

Finally, I want to thank you for the incredible work you are doing and your openness to respond to criticism! I might sound overly negative in my response here, but I am genuinely a great fan and longtime supporter of Veganuary and I do think that Vasco is definitely underestimating your impact. 

Edit: Spelling and small changes for clarity. 

Vasco Grilo🔸 @ 2025-03-04T11:03 (+2)

Thanks for the comment, @PreciousPig! I strongly upvoted it. I am tagging you because my initial comment only included the 2 sentences before this one.

Dear Team of Veganuary,

I am tagging @Toni Vernelli such that Veganuary's team knows about your comment (only the author of the post is notified of new comments by default).

I think there are some incredibly promising metrics about Veganuary’s success, for examnple this 2019 survey on why people go Vegan in which 12800 people participated, out of them 369 (a little under 3%) said that Veganuary was the first thing that seriously made them consider going Vegan.

"369 people [2.88 % (= 369/12,814) of the vegans surveyed] succesfully took part in Veganuary [being vegan for 1 month]". It does not follow that Veganuary caused these people to become vegan. Moreover, even if everyone who successfully took part in Veganuary became permanently vegan, they could have become so a little later anyway without Veganuary.

Nitpick. I wonder whether you are using "for example" to present your strongest argument for Veganuary being cost-effective. If yes, I think "crucially" would convey your views more faithfully than "for example".

If we assume this metric is accurate and still holds true today, and that roughly 1% of the people in Europe and North America are Vegan (or very roughly 10 milllion people out of 1 billion people), as many as 280 000 people might be Vegan today because of Veganuary. If we further assume each Vegan person saves on average one animal’s live a day, that would be 100 000 000 (100 million) animals spared each year due to Veganuary. 

The survey you linked to looked into 0.128 % (= 12.8*10^3/(10*10^6)) as many vegans as those you estimated exist in Europe and North America. So here is room for huge selection bias. The number of people successfully participating in Veganuary as a fraction of the number of vegans could be as low as 3.69*10^-5 (= 0.00128*0.0288) even if the data from the survey was 100 % reliable (athough highly selected).

Besides continuing to share the number of Email signups, here are some ways how I think you could increase / confirm the accuracy of the YouGov survey:

I would ask questions like these to random (representative) samples of the general population in the target countries:

  • How much more or less poultry meat would you have consumed in January without Veganuary?
  • How much more or less poultry meat would you have consumed in January without Plantuary?

The possible answers could be like these:

  • I consumed 100 % less poultry meat (I did not consume poultry meat).
  • I consumed 80 % less poultry meat.
  • ...
  • I consumed roughly the same poultry meat.
  • I consumed 20 % more poultry meat.
  • ...
  • I consumed 100 % more poultry meat (I doubled my consumption of poultry meat).
  • I more than doubled my consumption of poultry meat.

I would have similar questions for eggs, fish, and seafood besides fish. My suggested questions:

  • Focus on the animal-based products linked to the vast majority of animal suffering. They do not ask about whether people participated in Veganuary because what ultimately matters is whether they reduced their consumption of animal-based foods.
  • Include control questions about Plantuary, which sounds similar to Veganuary, but does not exist. The effect of Veganuary should be measured relative to that of the control campaign. I expect people will report reducing their consumption of animal-based products because of Plantuary, in the same way that 4 % of Americans report believing lizardmen are running the Earth.
  • Have continuous answers which offer more information. I am wary of questions which can only be answered as yes or no. Social desirability bias will prompt people to report decreasing the consumption of animal-based foods even if the decrease was negligible.

I think it would be great if Veganuary partnered with Faunalytics or the Humane and Sustainable Food Lab to run a rigorous survey.

Joseph Richardson @ 2025-03-01T18:06 (+9)

I'd add that your Veganuary participation numbers are likely way too generous. They come from a poll of the general public on participation and then scaling those numbers up to a broader population. However, opinion polling of this type famously overestimates the share of the population with rare characteristics due to mistakes, trolling, or in this case potentially social desirability bias. 

Indeed, I have the impression that surveys estimating the share of vegans in the US population often getting about 5%, which is around the lizardman constant. Objective purchase data suggests that the number is more like 1%.

Vasco Grilo🔸 @ 2025-03-01T18:54 (+3)

Nice to hear from you, Joseph! Great point. I have changed "participated in Veganuary" to "reported participating in Veganuary", which was what I meant. I have added the following to:

  • The summary and discussion. "I would also add a question to the survey used to determine the number of people who participated in Veganuary which would check whether the respondents are replying in good faith. This is important because only a small fraction of the population participates in Veganuary, such that small errors matter. 4 % of Americans believe (actually, report believing) lizardmen are running the Earth".
  • The section about the cost-effectiveness of Veganuary. "My effect size refers to people who reported participating in Veganuary. The number of people who actually participated may be significantly smaller. Veganuary concluded 25 M participated multiplying small fractions of participants in the surveyed countries by their populations. However, such fractions may be significantly explained by a few people mistakenly reporting their participation due to lack of attention or social desirability bias".
Toni Vernelli @ 2025-02-28T20:27 (+6)

I have tried to post Veganuary's reply twice now and the spam-blocker immediately deletes it. I do not have the intercom icon so I don't know how to contact the admin to get this resolved. I hope they will see this message and post my comment.

Dane Valerie @ 2025-02-28T21:00 (+3)

Apologies, Toni! We’ve restored your comment—it should be visible now.