Heroes and Cowards:

I'm delighted to report that Profs. Dora Costa and Matthew Kahn from the UCLA Economics Department will be guest-blogging next week about their new book, Heroes and Cowards: The Social Face of War. The book looks fascinating, and has gotten accolades from some top people both in military history (for instance, James McPherson, author of Battle Cry of Freedom) and in the social science of social relationships (for instance, Robert Putnam, author of Bowling Alone: The Collapse and Revival of American Community). "This remarkable book is destined to become a classic in social science," writes Putnam, who certainly knows things about classics in social science. "It addresses issues of supreme importance and timeliness -- loyalty, betrayal, heroism, cowardice, survival, the challenges of diversity, and the benefits of social bonds. It rests on rigorous statistical analysis of an extraordinary historical archive, and yet it is so readable as to be unputdownable. It deals with a single epochal event in one nation's history -- the U.S. Civil War -- and yet its lessons are highly relevant in many other eras and societies, including our own."

Here's a brief summary to get you an idea of the coming week:

When are people willing to sacrifice for the common good? What are the benefits of friendship? How do communities deal with betrayal? And what are the costs and benefits of being in a diverse community? Using the life histories of more than forty thousand Civil War soldiers, Dora Costa and Matthew Kahn answer these questions and uncover the vivid stories, social influences, and crucial networks that influenced soldiers' lives both during and after the war.

Drawing information from government documents, soldiers' journals, and one of the most extensive research projects about Union Army soldiers ever undertaken, Heroes and Cowards demonstrates the role that social capital plays in people's decisions. The makeup of various companies -- whether soldiers were of the same ethnicity, age, and occupation -- influenced whether soldiers remained loyal or whether they deserted. Costa and Kahn discuss how the soldiers benefited from friendships, what social factors allowed some to survive the POW camps while others died, and how punishments meted out for breaking codes of conduct affected men after the war. The book also examines the experience of African-American soldiers and makes important observations about how their comrades shaped their lives. Heroes and Cowards highlights the inherent tensions between the costs and benefits of community diversity, shedding light on how groups and societies behave and providing valuable lessons for the present day.


[Dora Costa and Matthew Kahn, guest-blogging, January 12, 2009 at 3:02am] Trackbacks
An Overview of Heroes and Cowards: The Social Face of War

The recent Bernard Madoff Ponzi scheme debacle highlights that social networks can impose costs. In a series of articles, the New York Times has sketched how a group of insiders, mainly wealthy Jewish families from the New York region, sought to invest in Madoff's investment fund. Trust in Madoff as a man may have reduced effort in conducting due diligence to investigate whether his returns were too good to be true.

Social networks also offer large benefits. Successful executives and academics network constantly. How much of the returns to attending an Ivy League university are due to access to valuable social networks rather than what one learns from leading professors? An Ivy League graduate named Caroline Kennedy may soon be named the U.S Senator from New York. Her family and social connections appear to distinguish her from other ambitious professional politicians seeking the same senate seat such as Carolyn Maloney.

The fundamental challenge for empirical social scientists who want to study the causes and consequences of social networks is to identify who is the same network and to collect data on important outcomes that could be plausibly affected by participating in a network. For the last seven years, we have focused on the causes and consequences of social networks in a distinctive setting: the U.S Civil War. 2009 is the 200th anniversary of Abraham Lincoln's birth. What can we learn about social networks and social capital by studying the lives of enlisted men who fought for the Union Army?

In our new Princeton University Press book, Heroes and Cowards: The Social Face of War, we examine the war experience for Union Army soldiers. We weave a single narrative from the life histories of 41,000 Union Army soldiers, diaries and letters, and government documents. Our core questions are not those typically asked in a military history. When are men willing to sacrifice for the common good? What are the benefits to men of friendship? How do communities deal with betrayal? And what are the costs and benefits of being in a diverse community?

One summer we both read Robert Putnam's thought-provoking book Bowling Alone. We were fascinated by Putnam's account of the decline in American civic engagement over time. Putnam emphasized the growing popularity of television as a pivotal cause of the decline in social capital and community participation, but we wondered whether an unintended consequence of the rise of women working in the paid labor market was that PTAs and neighborhood associations lost their "volunteer army." We started to write a paper testing whether the rise in women's labor force participation explained the decline in residential community participation. To our surprise, we found little evidence supporting this claim. Instead, our analysis of long-run trends in volunteering, joining groups, and trust suggested that, all else equal, people who live in cities with more income inequality were less likely to be civically engaged. These results contributed to a growing literature in economics documenting the disturbing fact that people are less likely to be "good citizens" when they live in more diverse communities.

In the summer of 2001, we realized that the American Civil War provided the ideal "laboratory" for studying the costs and benefits of social networks. The setting was high stakes - roughly one out of every six Union Army soldiers died during the war. Unlike people in civilian life today, Union Army soldiers could not pick and choose their communities. For each of the 40,000 soldiers we observe key outcomes and choices. If a man deserts, if a man dies in a POW camp, if a man survives the war but chooses not to move back to his county of enlistment after the war, we observe each of these choices and outcomes. By studying how the probability of each of these outcomes varies as a function of individual solider attributes and the characteristics of the 100 men in his war community (his company), we quantify the role of social networks in a high stakes setting.

In our next post we will discuss our unique data set and why it is so difficult to create such a data set today.


[Dora Costa and Matthew Kahn, guest-blogging, January 13, 2009 at 1:10am] Trackbacks
The Nobel Laureate Robert Fogel's Union Army Sample

In our new Princeton University Press book, Heroes and Cowards: The Social Face of War, we examine the war experience for Union Army soldiers during the U.S Civil War. The meat of the book is based on a statistical analysis of a unique data base. In this post, we would like to provide some details about this data base.

Our book would not have been possible without a monumental data collection effort that first began in 1981, led by Robert Fogel, the 1993 Nobel Laureate in Economics. How do you construct a longitudinal dataset from disparate sources and from the free-form letters, affidavits, and other documents that constitute a soldier's record in the National Archives? The data are publicly available here.

Beginning with one list of white volunteer units and one list of U.S. Colored Infantry Units, both sorted in random order, inputters collected basic descriptive information from the "Regimental Books" in the National Archives on all of the enlisted men in a company until the two samples consisted of roughly 1.6 percent of all whites (almost 6,000 men) and 1.6 percent of all blacks (almost 6,000 men) mustered into the Union Army. The men were then linked to their army records, stored in the National Archives. These records consist of compiled military service records and of cards containing medical records and vital statistics.

For example, John Nelson Cumbash of Company F, First Regiment USCI has a compiled military service record that consists of one company descriptive book card, one company muster-in roll card, fifteen company muster roll cards, one detachment muster-out roll card, and one company muster-out roll card. He has eight medical records cards. These record his enlistment, his promotion to sergeant and then his demotion, his absence on recruiting services, his hospitalizations for fever, exposure to cold, and chronic rheumatism, and his final muster-out. Linkage to the pension records (which constitute one of the most significant sources of health information on past populations) allows us to follow men until their deaths. John Nelson Cumbash's pension file is roughly three-quarters of an inch thick. Beginning in 1887 he filed four unsuccessful pension applications until he received a pension in 1897 which he collected until his death from pneumonia in 1901. His widow Mary filed for a widow's pension and much of the pension record details the investigation of her claim. Her claim was denied because she had not divorced her first husband before marrying John. Finally, linkage to pre- and post-war censuses provide snapshots of the soldier's family and occupation at fixed points in time. From John Cumbash's 1870 census record we learn that he was a waiter in a hotel, that his wife Sarah (his first wife) took in washing, and that he had two boys.

By randomly selecting Union War Companies and then conducting a 100% sample of all 100 men within each War Company, the Fogel data allows us to recreate each soldier's 24 hour a day live and work community. Back then, there were no televisions or Internet or cars, your fellow soldiers were your world. Some soldiers fought in homogenous companies while others fought in diverse companies.

ChrisIowa (btw, did we mention that Iowa had few deserters?) asked us, "Why was there diversity in companies?" All regiments were formed locally. We examined Civil War diaries and letters to identify six sources of diversity within companies. The volunteer infantry regiments consisted of 10 companies, each containing roughly 100 men, commanded by a captain and two lieutenants, who were often volunteer officers drawn from state militias, men of political significance, or other prominent men in the community. At the beginning of the war, men would enlist with one or several friends but rarely with fifty. Once companies were full, they would take no more men, and friends would need to find another company or regiment. Men's eagerness to get to the front led them to pick regiments thought to be departing soon. And they quickly left regiments that were late in departing, even enlisting in the regiment of another state. Later in the war, when the new recruits were not so eager, men might enlist in a distant town to receive a large bounty, adding to company diversity.

Although a company was generally not replenished with new men when disease, military casualties, and desertions whittled down its numbers, some states added new recruits to existing regiments and regiments whose members' three year terms were up were reconstituted with veterans and new men. Finally, the need to travel to recruiting stations increased company diversity. Farmers and farmers' sons had to travel to town to enlist. Small towns could not raise an entire company, so their men would enlist elsewhere and do so only with a few friends. Commissioned officers were responsible for finding their own men and often had to scour the entire state to fill their regiments.

Statements in soldiers' diaries and letters indicate that they were thrown together with strangers. Amos Stearns, who enlisted with five of his friends, lamented ``Life in the army was very different from life at home. In one place we could choose our companions and those we wished to associate with, but in the army how different'' (Kent 1976: 214-5). One soldier wrote home, ``We have a remarkable civil and Religious company. . . . i think it is a providencial circumstance that I enlisted in this company for I hear that there is desperate wickedness in very regiments i came so near enlisting in'' (letter of David Close, Nov. 4, 1862, 126th Ohio Volunteer Infantry, Company D.

From today's vantage point, the Fogel data set is extraordinary. Concern about identity theft and insurance companies using confidential information to cherry-pick healthy and low-risk patients would make it extremely difficult to build a similar dataset today. A researcher attempting to build an analogous data set for Vietnam veterans would need to obtain the consent of each man. But the types of individuals willing to grant permission would probably not be a random sample of the population. And, despite the well-publicized stories of men buying their way out of the draft, the white sample is representative of the Northern population of military age in terms of wealth and literacy rates. Only in World War II were service rates higher.

In our next two posts, we will discuss the key findings and hypotheses we tested using the military data base. Today a historian has reviewed our book in the Wall Street Journal.


[Dora Costa and Matthew Kahn, guest-blogging, January 14, 2009 at 12:20am] Trackbacks
Social Networks during War Time:

In our new Princeton University Press book, Heroes and Cowards: The Social Face of War, we examine the war experience for Union Army soldiers. We weave a single narrative from the life histories of 41,000 Union Army soldiers, diaries and letters, and government documents. Our core questions are not those typically asked in a military history. When are men willing to sacrifice for the common good? What are the benefits to men of friendship? How do communities deal with betrayal? And what are the costs and benefits of being in a diverse community?

In this post and our next post, we would like to provide an overview of some of our key findings. For readers who enjoy applied econometrics, we encourage you to go Dora Costa's UCLA website where you can download our key academic papers.


A soldier who sought to survive the U.S Civil War should have deserted and roughly 200,000 Union Army soldiers did (about a tenth of the army). Out of the roughly 80,000 men who were caught, 147 were executed. Those who stayed faced a death rate of 14 percent, with half of the deaths from wounds and half from disease. In contrast, during World War II, Stalin's armies had special detachments that formed a second line to shoot at any soldiers in the first line who fled and the families of all deserters were also arrested. Out of the roughly 35,000 German soldiers tried for desertion by the Third Reich, about 22,750 were executed. Democracies cannot inflict such punishments. Lincoln recognized that "you can't order men shot by the dozens or twenties. People won't stand it."

Given these facts, is it surprising that only a tenth of men actually deserted? We argue that desertion is a great measure of "community participation". In a group of 100 men, if one man deserts the army he raises his probability of survival but puts his fellow men at risk to be crushed by the enemy. Unlike in the modern corporation with bonus pay and pay for performance, the diaries these men left makes clear that they were fighting for each other.

We use our unique longitudinal data to document several facts about the determinants of desertion. Here we focus on our most salient findings. We encourage you to read our book to learn all! In what follows, please keep in mind that these findings are based on multivariate statistical analysis so we are holding all other factors constant and varying one explanatory variable at a time. When the Union Army was winning battles, desertion rates declined. Just like in professional sports, everyone loves a winner. Desertion probabilities were higher in more diverse war companies. Turning this statement around, men who fought in more homogenous war companies (based on occupation, age, and place of enlistment) featured lowered desertion probabilities. A generalization of this finding is that people are better citizens in social settings when their community looks like them. In our next post, we will relate this finding to ongoing social science research on the costs of living in a diverse community.

Surviving POW Camps

Many of us have enjoyed watching Hogan's Heroes on television. While Bob Crane outwitted Clink and Sgt. Schultz in his WW2 Nazi POW camp, U.S Civil War soldiers sent to Andersonville had a lot less fun. An estimated 211,411 Union soldiers were captured during the Civil War. Seven percent of all U.S. Civil War soldiers were ever imprisoned compared to 0.8 percent for World War II.

Civil War POWs suffered from poor and meager rations, from contaminated water, from grounds covered with human excrement and with other filth, from a want of shoes, clothing, and blankets (having often been stripped of these by needy Confederate soldiers), from a lack of shelter in the open stockades that constituted camps such as Andersonville and Millen, from the risk of being robbed and murdered by fellow prisoners, and from trigger-happy guards. Our data show that at Andersonville, the most notorious of the POW camps, roughly 40 percent of all men of who passed through the camp died, and half of the deaths occurred within three months of entry. The chief causes of death were scurvy, diarrhea, and dysentery.

How did men survive such horrific conditions? The accounts of survivors provide some clues, as do the accounts of survivors of Nazi concentration camps, the Soviet gulag, and Japanese and Vietnamese POW internment camps. But some accounts conclude that death is random; others emphasize psychological defense mechanisms; others emphasize the importance of leadership; and still others emphasize the role of friends. We can use our longitudinal data and a data set on almost the entire population of Andersonville put together by the Park Service to examine the effects of age, social status, rank, camp population, and the presence of own officers on survival.

The single most important determinant of camp survival was how crowded the camp was. Another important determinant of camp survival was age. Those of higher rank fared better, as did those with useful skills. Men with officers from their own companies were more likely to survive than those without or with fewer officers.

Holding these factors constant, social networks within the camps increased a soldier's survival probability. We can establish this because we know each POW's war company and home town. We document that men who were in the camp with "more friends" had higher probabilities of survival then men with similar demographics who were in the camp with fewer friends. Ties between kin and ties between comrades of the same ethnicity were stronger than ties between other men from the same company.

Why did friends increase the probability of surviving POW camps? Did friends provide extra food or clothing, tend to the sick, protect against the predation of other prisoners? Or did simply having a friend have a positive effect on men's immune and endocrine systems? Monkeys randomly assigned to stable or unstable social conditions and inoculated with the simian immunodeficiency virus face shorter lives if they live in unstable social conditions conditions. We cannot run such tests on humans. But, in our final post, we will discuss some intriguing evidence for how social networks can cushion psychological shocks. We would like to conduct similar survival research based on records from the Nazi holocaust camps. We have not been able to identify credible network measures (analogous to our War Company identifiers) to be able to establish who knew who within these camps.


[Dora Costa and Matthew Kahn, guest-blogging, January 15, 2009 at 12:08am] Trackbacks
Social Networks and Their Impact after the U.S Civil War

Our last post sketched some of our key findings concerning the role of social networks and their effects on desertion and surviving POW camps during the U.S Civil War. In our new Princeton University Press book, Heroes and Cowards: The Social Face of War, we also use our unique longitudinal data to explore how the war affected the later life experience for Union Army soldiers. In this post, we discuss how deserters who survived the war lived their lives after the war. We also discuss our findings concerning black troops.

Deserters: Shame and Ostracism

During the U.S Civil War, home towns knew which of their sons had fought honorably and who had deserted. Spitzer and Avatar both commented that the need to maintain their reputations would keep men from deserting. And, as Spitzer predicted, we found that men from large cities were more likely to desert, all else equal. Spitzer then asked what happened to the deserters. After the war, would the cowards be welcomed back to their hometowns? Or would they feel shame and experience ostracism that would push them to move away?

If deserters left home, it was not because of written laws, but because of community mores. Once the war was over, deserters who had not been pardoned during one of the wartime presidential amnesties were dishonorably discharged with forfeiture of pay. They could return home without fear of arrest, but were deemed by the Federal government to have relinquished their citizenship or right to become a citizen of the United States and therefore their voting rights. Later court interpretations weakened federal law even further by specifying that the requirement could not be desertion alone but had to be a conviction of desertion. Furthermore, because states regulated voting rights, this federal disenfranchisement was widely viewed as ineffectual except in the territories and in the states that passed laws disenfranchising deserters (Lonn 1928: 202-207; United States War Department. 1880-1901. Series III, Vol. 5, 1900: 110).

By 1880 only Vermont still disenfranchised deserters. In Kansas, an 1866 amendment to the state constitution revoked voting rights from those dishonorably discharged as well as from felons and people who had aided in the rebellion, but an 1874 amendment struck dishonorable discharge as one of the listed offenses that led to a revocation of voting rights.

In thinking about the role of social sanction as a means to discourage desertion, we have been highly influenced by Robert Ellickson's Order without Law. He argued that social sanction can substitute for formal legal sanction in encouraging law and order. Individuals adhere to community codes of conduct either because of laws and legal punishments or because of systems of informal social control. The community can enforce social norms if it knows who fought honorably and who did not (and this was well known to all Civil War communities) and if it is willing to punish those who dishonored the community. "An enforcer is on the front line of the system of informal social control. Enforcers observe what actors do and respond by meting out calibrated rewards and punishments" (Ellickson 2001: 8). But enforcers are not compensated for their actions, so why would they punish? Communities that were pro-war supplied a disproportionately large number of soldiers who fought and died in the war. Raw emotion and anger at the men who dishonored the community and endangered their comrades would motivate community enforcers.

Using our longitudinal data base, we found 7,000 Union Army survivors in the 1880 census. We use this long run evidence to document three key facts. Relative to non-deserters, and return deserters, deserters were less likely to move back to their home county and state after the war. These men were also less likely to be found in the 1880 census. This indicates that they changed their names and their identities after the war. Finally, we document that deserters who were from pro-War counties were even less likely to move home after the War. We measure a county's pro-War sentiment based on the share of its voters who voted against Lincoln in the 1864 Presidential Election.

Black Soldiers: The Costs and Benefits of Diversity

Our sample of 6,000 black soldiers who fought for the Union Army allows us to examine the short run costs and long-run benefits of fighting in a diverse company. These troops represented a mixture of free men and ex-slaves who fought together in segregated all black units (with white commissioned officers). Within these black companies, soldiers differed with respect to their birth cohort and their county and state of enlistment. Similar to our results on desertion for white soldiers, we document that black soldiers were more likely to desert when they fought in more heterogeneous companies (based on geographical diversity and birth cohort). They were less likely to desert when fighting with men from the same plantation. These results suggest that black soldiers were more loyal to their unit when they fought in companies with men who had similar backgrounds.

We recognize that there are long run benefits from exposure to such diversity. After all, we can only learn from people who have had different experiences than we have had. We document that the black ex-slaves who fought with free men were more likely to become literate and were more likely to move to states after the war where their fellow company mates enlisted from. They were also more likely to drop their slave names, a sign that they were adopting a freeman's identity. Our findings on the short run costs but long term benefits of exposure to diversity echo the points made by modern advocates of affirmative action on university campuses today.

What Sort of Diversity Matters?

The River Temoc asked how we measured homogeneity. For white soldiers we looked at place of birth, occupation, and age cohort. For black soldiers we looked at place of birth, age cohort, and, for the slaves, whether they were from the same plantation. What mattered most? For black soldiers, it was place of birth. For white soldiers, it was occupation. (This echoes our finding that in modern day communities income inequality is more important determinant of volunteering, joining nonchurch organizations, and trust than ethnic or racial diversity).

Dasarge noted that unit cohesion is mostly a psychological issue and that while race, home areas, and religion all play roles, they are not determinative. Yes, our work emphasizes the importance of ethnicity, state of birth, occupation, age, and kinship in unit cohesion in the past. We are not claiming that these were the only factors that influenced the formation of social ties among Union Army soldiers. Nor are we claiming that these factors are as important now as they were in the past. Race and ethnicity no longer predetermine friendships and marriage. For example, in the nineteenth and early twentieth century, Asians were viewed as "forever foreigners," but marriages between whites and Asians have become increasingly common. Although black-white marriages are still rare, they are increasingly steadily. Even religion has become less important. What does seem to be becoming more important for volunteering, group participation, and trust is income diversity. And, one of the big determinants of income is education. Has education become the new social divide?

We recognize that highlighting the cohesion costs of diversity is not a politically correct statement. In his 2006 Johan Skytte Prize Lecture, Robert Putnam discusses his empirical analysis of modern day civic engagement in America. He reaches similar empirical conclusions on the consequences of diversity. He devotes ample attention to encouraging bridging social capital across groups. We hope that President-Elect Obama will point to his own diverse upbringing to start a national dialogue on this awkward issue. While the ongoing financial crisis has crowded out this issue in recent months, immigration and income inequality raise key policy issues in many nations around the world.


[Dora Costa and Matthew Kahn, guest-blogging, January 16, 2009 at 12:03am] Trackbacks
Empirical Social Networks Research

In this last blog entry, we would like to respond to some commentators and discuss our new research on the consequences of social networks. Dasarge and Fischer both discuss leadership. We can find some evidence of the importance of leadership. Black soldiers with an abolitionist officer were less likely to desert. But this was less important to their desertion decision than being in a company with guys like them. So to in response to Richard Aubrey, if you wanted to keep your men from deserting during the Civil War (and keeping men from deserting is a good idea if you want to win a war) having a homogeneous unit was the most important factor we could identify. We also find that men who had more of their (non-commissioned) officers in Andersonville were more likely to survive. Officers divided up the rations. We'd like to do more to identify the effects of leadership but our problem is identifying a good leader versus a bad one.

Our new research builds on the insights presented in our recent Heroes and Cowards book. We are convinced that empirical work on social networks offers social scientists with an interdisciplinary inclination to work together. Recently, sociologists, economists, political scientists and legal scholars have all made important contributions to this field.

Research on terrorist organizations indicates that friends and relatives join together and work together. By one estimate, roughly three quarters of mujahedin joined the global Salafi Jihad (of which Al Qaeda is a part) either as a group with friends or relatives or as men with close social ties to members (Sageman 2004: 114). Seventy percent of captured Italian Red Brigade terrorists had joined a friend who was in the terrorist organization -- a next-door neighbor, a school friend with whom he or she had spent vacations, or a cousin with who belonged to the same voluntary association (della Porta 1988). Social bonds, not a shared terrorist ideology, drove the decision to join. The ideology came later (Sageman 2004: 133).

The fundamental challenge in conducting social networks research is to identify who is a member of one's network and what might be the causal mechanism such that participating in such a network causes a behavioral change. Critics will always raise the valid point that people are rarely randomly assigned to a network. Do greens choose to live in Berkeley, California (selection) or does living in Berkeley cause one to embrace environmentalism (treatment)? The gold standard for separating "selection effects" from "treatment effects" is to identify situations when group members have been randomly assigned to a group. This randomization mitigates concerns about self-selection. The 2006 book, Are Judges Political? by Cass Sunstein et. al. highlights how legal scholars have approached these issues.

An ongoing health research agenda has linked social networks to health. People who report themselves to be socially isolated, both in the number and quality of their personal relationships face a higher mortality risk from all causes and from several infectious, neoplastic, and cardiovascular diseases. A large body of literature links stress, whether in the form of war, natural disasters, divorce, lack of control on the job, or even disrupted sleep patterns, to cardiovascular disease. Social networks could either mitigate or accentuate the effects of stress. They could mitigate the effects of stress through beneficial effects on psychological and physical well-being. But, they could accentuate the effects of stress if the stressor leads to the loss of friends or family (e.g. the well-established effect of death of a spouse on the mortality of a survivor).

In a forthcoming Demography paper, we investigate the interaction between stress and social networks in one of the few human populations to provide us with measures of stress, of long-run outcomes, and of exogenous social networks. We find that being in a more cohesive company reduced the negative, long-term consequences of wartime stress on older age mortality and morbidity, particularly from cardiovascular causes. Focusing on the role of stress factors in health and mortality may be a fruitful line of research, particularly as we exhaust the gains from public health advances. Matthew Kahn has returned to conducting research on environmental economics topics. While the U.S Civil War might appear to be light-years removed from urban pollution and Global Warming, social capital actually ties these sets of issues together. After all, there would be no "tragedy of the commons" if people felt altruism for each other and internalized the social costs of their actions ranging from littering to driving a Hummer around. In societies where there is greater social capital, there is less need for formal enforcement of anti-pollution laws. Social networks also can play an important role in the diffusion of new green products. If one's probability of buying a hybrid vehicle or solar panels is an increasing function of whether one's neighbors are purchasing such green products, then "bandwagon" effects can help to mitigate the challenge of climate change. Friends may also more quickly learn from their friends' experience with new unproven products. Such word of mouth learning will accelerate the diffusion of good ideas.