Spillovers of Pro-Social Motivation: Evidence From a Randomised Intervention Study on Blood Donors

Lambert here: “Giving” blood. How irrational. No good neo-liberal would ever do such a thing! And what is this curious notion of “good citizenship”?

By Adrian Bruhin, Assistant Professor of Economics at HEC Lausanne, University of Lausanne, Lorenz Götte, Professor of economics, Universities of Bonn and Lausanne, Simon Haenni, PhD student in economics at HEC Lausanne, University of Lausanne, and Lingqing Jiang, PhD student in economics at HEC Lausanne, University of Lausanne. Originally published at VoxEU.

Evidence suggests that people are more likely to behave in a pro-social way if they are aware of others who behave in such a manner. This column finds evidence for this phenomenon among blood donors. For every unit increase in a donor’s motivation, there is a 44% spillover in motivation to their fellow tenant. There is an overall increase in donation rates due to such a social multiplier of 17.9 percentage points, instead of the 10 percentage points obtained by calling an isolated donor.

Understanding Pro-Social Behaviour

Pro-social behaviour, i.e. acting voluntarily in the interest of the common good even if it comes at a personal cost, is an important part of a well-functioning society (Putnam 2000, Durlauf 2002). Donating to charity, giving time as a school board member, volunteering to help at a public event, not dropping litter, even voting in elections; it is the myriad of everyday acts of public service and good citizenship that help maintain the fabric of a productive and prosperous society. Researchers and policymakers alike have strived to understand this type of behaviour and find effective ways to promote it. Yet, despite the attention given to understanding and promoting good citizenship, it is still not clear what policy interventions are most effective.

There is some evidence from existing research, suggesting that people are more likely to behave in a pro-social way if they are aware of others behaving in a similar manner (Falk and Fischbacher 2002, Fehr and Fischbacher 2004, Frey and Meier 2004, Shang and Croson 2009). And the motivation to act pro-socially may spill over from one individual to another in social networks where individuals are linked through social ties (Granovetter 1973, Goette et al. 2006, Twenge et al. 2007, Leider et al. 2010). If pro-social motivation spills over between individuals, any intervention that affects individual motivation will feed back into the community and will have a larger aggregate effect akin to the Keynesian consumption multiplier.

Motivational Spillovers: New Evidence from Blood Donors

In a recent paper, we address the possibility of motivational spillovers for the case of blood donations (Bruhin et al. 2015). Blood donations are another textbook example of pro-social activity. Donating blood is a voluntary act where the donor receives no material reward and bears the personal cost of giving blood, while society at large benefits from a sufficient stock of whole-blood transfusions. Many interventions to foster donation rates have previously been examined, ranging from material and immaterial incentives to different forms of appeals to donors (Ferrari et al. 1985, Goette et al. 2009, Lacetera et al. 2012, Niessen-Ruenzi 2014). Even though information about incentives seems to spread among blood donors (Lacetera et al. 2014), no evidence exists on the relevance of motivational spillovers for blood donations.

We examine the donation behaviour of donors registered with the Blood Transfusion Service of the Red Cross in Zurich, Switzerland. Our data span the period from April 2011 to January 2013, during which time donors were repeatedly invited to blood drives – time-limited events to collect blood. We focus on dyads of donors who are likely to share strong social ties, as they live at the same address and there is no more than 20 years difference in ages between them. About two-thirds of the dyads are couples living together, while the rest are other cohabitants, or neighbours living in the same building. In total, we observe 3,723 such dyads and 20,240 individual donation decisions.

One significant challenge, well known in econometrics, is isolating the impact of spillovers on the motivation to give blood as opposed to, for example, the impact of environmental factors or personal characteristics that both people in a dyad have in common (Manski 1993). If two individuals behave the same way, it may just be because they are exposed to the same environment, not because they influence each other. As it turned out, a feature of the data allowed us to solve this challenge. A random subset of donors received an additional call to their mobile phone, during office hours, two days before a blood drive, telling them their blood type was in short supply and urging them to donate. Previous research shows that donors receiving such a phone call are about 8 or 9 percentage points more likely to donate blood than donors who do not receive such a phone call (Bruhin et al. 2015).

The randomised phone call allowed us to cut through the environmental influences and to isolate the effect of motivational spillovers because it only directly impacts the motivation of the person being called and not the motivation of their fellow tenant. If the fellow tenant who is not directly affected shows an increase in her or his probability of donating following that phone call, it can be attributed to motivational spillovers. We also verified that it is really the phone call recipient’s motivation to donate that spills over, and not the information about a particular blood type being in short supply.


  • We found that they render policy interventions much more effective. For every unit increase in a donor’s motivation, there is a 44% spillover in motivation to their fellow tenant.

The resulting increase in the fellow donor’s motivation then spills back, resulting in a positive feedback loop. This positive feedback loop creates a social multiplier of 1.79 for any policy motivation that greatly enhances its effectiveness. Take, for example, the phone call intervention we used in our paper. Its effect is to increase turnout by approximately 10 percentage points if an isolated donor is called. This is also what our estimates imply from using the dataset on fellow tenants, if we ‘shut down’ the channel of motivational spillovers. When we examine how motivational spillovers change this response, we find that this amplifies the response of the donor being called, and also generates a substantial effect on the follow tenant.

  • As Figure 1 shows, the donor called is now 12.5% more likely to donate, and his or her fellow tenant is 5.4% more likely to donate.

Figure 1. Effect of a phone call on the called donor and his or her fellow tenant

goette fig1 4 sep

Note: Panel a) shows that the donation rate of a donor increases by 12.5 percentage points on average if the donor receives a phone call. Panel b) illustrates that the fellow tenant’s donation rate also increases by 5.4 percentage points on average if the donor receives a phone call. The overall increase in donation rates is thus 17.9 percentage points. (The bars show the 95% confidence intervals).

It amounts to an overall increase in donation rates due to this social multiplier of 17.9 percentage points, instead of the 10 percentage points obtained by calling an isolated donor.

Concluding Remarks

The significance of these findings extends beyond blood donations. Given that it is the motivation cascading and feeding back from one person to another, it seems feasible that the social multiplier effect might extend to other interventions within an organisation or society designed to motivate a particular type of behaviour. Therefore, those interventions would benefit from targeting social groups – project teams, or intra-organisational networks and clubs, for example. However, it is important to note that we are not claiming that such spillovers apply beyond pro-social behaviour and further research would be required to confirm a comparable social multiplier effect in other domains.

For policymakers, what our research highlights for sure is that efforts at encouraging good citizenship, whatever the particular activity they are hoping to boost, should be directed at affecting the motivation of individuals in social groups. Motivational interventions targeted at couples, friends, families, club members, or church congregations, for example, are likely to be more efficient and effective than targeting independent individuals. Harnessing a network effect, by utilising social ties, policymakers can leverage the motivational impact of policy interventions designed to promote good citizenship.


Bruhin, A, L Goette, A Markovic, A Roethlisberger, R Buchli and B M Frey (2015), “Call of Duty: The Impact of Behavioural Interventions on Blood Donations.” Transfusion forthcoming.

Durlauf, S (2002), “On The Empirics Of Social Capital,” The Economic Journal 112(483):F459–F479.

Fehr, E and U Fischbacher (2004), “Social norms and human cooperation,” Trends in cognitive sciences 8(4):185–190.

Falk, A and U Fischbacher (2002), “Crime in the lab-detecting social interaction,” European Economic Review 46(4):859–869.

Ferrari, J R, R C Barone, L A Jason and T Rose (1985), “The use of incentives to increase blood donations,” The Journal of social psychology 125(6):791–79

Frey, B S and S Meier (2004), “Social comparisons and pro-social behaviour: Testing” conditional cooperation” in a field experiment,” American Economic Review 95(5):1717–1722.

Goette, L, D Huffman and S Meier (2006), “The Impact of Group Membership on Cooper- ation and Norm Enforcement: Evidence Using Random Assignment to Real Social Groups,” American Economic Review 96(2):212–216.

Goette, L, A Stutzer, G Yavuzcan and B M Freydur (2009), “Free Cholesterol Testing as A Motivation Device in Blood Donations: Evidence from Field Experiments,” Transfusion 49(March):524– 531.

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Niessen-Ruenzi, A, M Weber and D M Becker (2014), “To Pay or Not to Pay-Evidence from Whole Blood Donations in Germany,” Working Paper.

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About Lambert Strether

Readers, I have had a correspondent characterize my views as realistic cynical. Let me briefly explain them. I believe in universal programs that provide concrete material benefits, especially to the working class. Medicare for All is the prime example, but tuition-free college and a Post Office Bank also fall under this heading. So do a Jobs Guarantee and a Debt Jubilee. Clearly, neither liberal Democrats nor conservative Republicans can deliver on such programs, because the two are different flavors of neoliberalism (“Because markets”). I don’t much care about the “ism” that delivers the benefits, although whichever one does have to put common humanity first, as opposed to markets. Could be a second FDR saving capitalism, democratic socialism leashing and collaring it, or communism razing it. I don’t much care, as long as the benefits are delivered. To me, the key issue — and this is why Medicare for All is always first with me — is the tens of thousands of excess “deaths from despair,” as described by the Case-Deaton study, and other recent studies. That enormous body count makes Medicare for All, at the very least, a moral and strategic imperative. And that level of suffering and organic damage makes the concerns of identity politics — even the worthy fight to help the refugees Bush, Obama, and Clinton’s wars created — bright shiny objects by comparison. Hence my frustration with the news flow — currently in my view the swirling intersection of two, separate Shock Doctrine campaigns, one by the Administration, and the other by out-of-power liberals and their allies in the State and in the press — a news flow that constantly forces me to focus on matters that I regard as of secondary importance to the excess deaths. What kind of political economy is it that halts or even reverses the increases in life expectancy that civilized societies have achieved? I am also very hopeful that the continuing destruction of both party establishments will open the space for voices supporting programs similar to those I have listed; let’s call such voices “the left.” Volatility creates opportunity, especially if the Democrat establishment, which puts markets first and opposes all such programs, isn’t allowed to get back into the saddle. Eyes on the prize! I love the tactical level, and secretly love even the horse race, since I’ve been blogging about it daily for fourteen years, but everything I write has this perspective at the back of it.


  1. PlutoniumKun

    Is this really new? I recall years ago reading research on littering, waste collection and recycling indicating that appeals to individual conscience rarely works – to get people to take up new, more socially aware habits involves a mix of compulsion and persuasion, up to a point where it becomes the ‘norm’, and take-up rates increase enormously. As so often, economists pick up ideas which have long been around and well studied in sociology or psychology, and then present them as if they are new.

    Having said that, it is good that economists are at last realising there are other processes in the world other than the price mechanism. When I first visited the US from Ireland, I was astonished to find that blood donations were paid for, and as a consequence most blood products seemed to come from the poorest of the poor, while regular people almost never contributed. It was the exact opposite in Ireland (and most of Europe), where the most you would get would be a snack (or if lucky, a bottle of Guinness) in exchange for giving blood, but there was never any shortage of donors – it was simple something nearly everyone did.

    1. vegeholic

      i think you are misinformed. where i live (indiana) all blood donations are voluntarily given by regular people. i have not heard of payments for such donations. that said, i am curious about comments below regarding overpaid blood bank executives. i am sure the phlebotomists who are doing the sticking are not getting rich.

      1. tegnost

        plasma pays 280 a month according to the ad in the bus, but you have to sign a release that if they kill you it’s nobody’s fault but your own…

      2. albrt

        Whole blood in the US is almost always donated. Whole blood donations started in an earlier era when they didn’t have much in the way of screening technology, so they didn’t want to encourage donations from skid row.

        Plasma donation developed later and is almost always paid (and is usually located on skid row).

  2. oho

    a bit tangential, but a bit conflicted about the blood donation industry.

    Yes, you’re making a donation and helping someone. BUT the blood banks, though generally non-profit, have reportedly ginormous margins. hence your “donation” in reality just pads the pay of the blood bank execs.

    but you do get a cookie, juice and the sticker.

    1. washunate

      Yeah, it makes me wonder if blood donation in Switzerland is a different situation? In the U.S. context, it’s a business. The American Red Cross alone raises billions of dollars annually as a middleman selling blood to the hospitals and others that actually use it.

  3. human

    This should be self-evident and is the very reason why honest, unbiased reporting of large populist events are not seen on front pages, above the fold!

  4. TheCatSaid

    While the comments about about donating blood are interesting, they miss the point of the post.

    The point was that if you want to support any non-self-serving activity that benefits society at large, research shows you’ll be more effective if you reach out to people who are meaningfully connected to one or more others, because the multiplier effect is significant.

  5. afisher

    1. Blood is “free” . There is a charge for the processing and handling of each blood donation and that cost is passed on the the hospital, which then passes it on to the patient that receives the blood components
    2. The processing is all the tests that are performed on each unit of whole blood collected and all the records and checks to assure that the Unit (and its components) are labelled correctly – as in correct blood type.
    3. As a professional in the blood bank “industry”, my job was to assure that the blood component that was dispensed / transfused to the patient did not kill them. To say that the industry is not complex is an understatement and it continues to evolve and grow as scientists learn more about uses for tissue and bones from donors ( yes most Blood Banks / Transfusion Services do all the tracking and tracing of tissue, bones and blood donations in case of an after the fact- transfusion/ transplant).

    Anyone attempting to argue about charges – may not understand the industry- my understatement.

    As to the altruism – on this date (9/11), one only has to remember how blood banks across the nation were inundated by people wanting to donate blood as a result of the event in NYC. My hospital in San Antonio, TX collected blood from over 200 patients.

    Most in the industry knew at the time that they blood would not be used on survivors- and as a matter of fact, the FDA modified the rule to allow the thousands of units of red-blood cells to be frozen ( a huge time, labor and monetarily expensive process) so that the ARC would not get a black eye for accepting donations only to have most of the RBCs to be trashed 45 days later. And note – we did not freeze or discard any RBC’s as we are a major Trauma center f 5 counties in South Texas.

    Blood Banks are not Plasma Centers – 2 entirely different animals, different license, different use of blood components, etc.

  6. RBHoughton

    There is something you may have overlooked Lambert, excuse me.

    The Nebraska Diet Heart Survey and the Kuopio Ischaemic Heart Disease Risk Factor Study in Finland both revealed that giving blood occasionally significantly reduces the risk of arterial disease, stroke and heart attack.

    The authorities you mention post-date analyses of the two studies above – Meyers et al of the Nebraska data in 1997 and Salonen of the Finnish data in 1998.

    One might speculate that the incidence of heart disease took off in Western society after the use of bleeding was abandoned by the medical profession.

    There is a substantial self-interested reason for blood donors to donate.

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