Racial animus can affect welfare in measurable ways, as economists have pointed out since the seminal work of Becker (1957) . Recent papers have shown that racial animus can hinder economic development, affect political institutions, and induce social unrest. 2 To prevent further fueling of racial animus and reduce its damage on the society, it is fundamental to rigorously identify how racial animus forms and spreads.
The coronavirus (Covid-19) pandemic provides a natural experiment allowing us to study why and how racial animus against certain groups can rise rapidly. It has long been argued that infection risk can foster xenophobia (Schaller and Neuberg, 2012) . While Covid-19 may originate from China, the Centers for Disease Control and Prevention (CDC) has emphasized that people of Asian descent are at no greater risk of spreading the virus than are other Americans. Nonetheless, since the outbreak of the virus, multiple incidents of Asian Americans being verbally or physically attacked have been reported by major news outlets. 3 , Hundreds more have been recorded by organizations that track hate incidents (Mullis and Glenn, 2020).
These are telltale signs that the current pandemic could have sparked racial animus against Asians. The challenge is to measure and understand this phenomenon rigorously and expediently.
In this paper, we exploit variation in the timing of the first local Covid-19 diagnosis across regions in the United States to causally identify how infectious diseases can trigger racial animus against Asians. We focus on the timing of the first Covid-19 diagnosis for two reasons. First, the first diagnosis in an area represents a salient increase in the infection risk. Lab experiments have shown that more salient threat of infectious diseases leads to stronger xenophobia (Faulkner et al., 2004) . Second, the exact timing of the first diagnosis is plausibly exogenous ---whether an area has its first diagnosis this week or the next is largely unpredictable and is unlikely to be correlated with other factors simultaneously changing local racial animus. 4 To proxy for an area's racial animus against Asians, we use the percentage of Google searches and Twitter posts (tweets) that include the word "chink" or "chinks". The proxy based on Google searches was first used by Stephens-Davidowitz (2014), who shows a negative relationship between an area's Google search rate of the word "nigger" or "niggers" and the vote share for Barack Obama in 2008, even after controlling for a number of demographic, economic and political variables. This proxy can capture hidden racial animus as searches are mostly private and unlikely to suffer from social-censoring. It has since been used to measure racial animus in papers like Anderson et al. (2020) and Depetris-Chauvin (2015) and been shown to have a positive relationship with economic downturn and anti-African American hate crimes (Anderson et al., 2020) . To capture public display of racial animus, we use a proxy based on public tweets, which has been used by Nguyen et al. (2018) among others to measure sentiment towards minorities.
We focus on the use of the c-word, because this is the most salient racial slur against people of Asian descent and is unambiguously pejorative. 5 Indeed, Google searches and tweets including the epithet are mostly negative. "Chinked eye" and "chink virus" are common terms in racially charged Google queries, and over 53.4 percent of racially charged tweets are categorized as showing "anger" or "disgust" between November 2019 and April 2020. Moreover, an area's monthly Google searches for the epithet is positively correlated with monthly anti-Asian hate crimes between 2014 and 2018 and negatively correlated with monthly visits to Chinese restaurants between 2018 and 2019, even after controlling for area fixed effects and year-month fixed effects.
Our first main finding is that the Covid-19 pandemic leads to a surge in racial animus against Asians. In the week after the first local Covid-19 diagnosis, racially charged Google search rate increases by 22.6 percent of the area's maximum search rate over the sample period, and racially charged Twitter post rate increases by 100 percent of its average over the sample period. The result is robust to excluding earlyand hard-hit states and to controlling for area fixed effects, year-month fixed effects, the severity of local Covid-19 infection, and an area's use of terms that are related to the c-word but are neutral in connotation, such as "Asian(s)", "Asia", or "China".
Analysis using unique Twitter user identifiers reveals that the increase in racially charged tweets mainly comes from existing Twitter users who post the racial epithet for the first time rather than those who have previously used the term. In the four weeks after the first local diagnosis, 2,064 Twitter users, who are not newly registered, tweet the epithet for the first time, potentially exposing their four million followers to racially charged content. This can create an multiplier effect on racial animus via persuasion (DellaVigna Next, we turn our attention to the factors fueling racial animus. First, fear of infectious diseases could 5 According to Philadelphia Bar Association (2014), the racial slur "originated in the 19th Century as a racial slur against people of Chinese descent", yet "is now widely used throughout the United States as a racial slur against people of Asian descent." The racial slur is as racist and hurtful to Asian Americans as the n-word is to African Americans (Richburg, 2008) . Importantly, this racial slur has not been reclaimed by the Asian American community, as exemplified by the 2018 incident when TBS analyst Ron Darling, who himself is of partial Chinese descent, had to quickly issue a public apology after receiving criticism over his use of "chink in the armor" when referring to the performance of a Japanese pitcher playing for New York Yankees. motivate racial animus. Evolutionary psychologists have argued that the desire to avoid harmful communicable diseases contributes to contemporary prejudices against subjective outgroups (Schaller and Neuberg, 2012) . Surveys by Binder (2020) and Gallup (Saad, 2020) document that most Americans were worried about contracting Covid-19, suggesting that fear of the disease indeed exists in the United States.
Second, the salience of the connection between Covid-19 and the Asian population is also a key factor. We find that the increase in animus is directed at Asians rather than other minority groups. Moreover, this racial animus is stronger on days when the connection is more salient, as proxied by President Trump's tweets mention China and Covid-19 at the same time. That time series relationship remains robust, even after we control for the severity of the pandemic and for general attention to Asians. Third, we find little evidence that the negative economic impact of the pandemic motivates the initial increase in racial animus. Areas bearing more severe economic impact of the pandemic do not exhibit a higher increase in racial animus than Americans. In addition, evolutionary psychologists argue that fear of and desire to avoid health threats can motivate racial bias (Schaller and Neuberg, 2012) . Earlier studies are mostly correlational based on surveys (e.g., Kim et al., 2016) or are established only in lab settings (Faulkner et al., 2004 ; O'Shea et al. 2020). We contribute by providing casual evidence that fear of infectious diseases and its link to a certain group lead to animus against the group while the economic impact of the disease plays a weaker role. terms when talking about the pandemic. One exception is the paper by Bartoš et al. (2020) . They use a controlled money-burning task among subjects in the Czech Republic to show that elevating the salience of Covid-related thoughts magnifies hostility against foreigners living in Asia. We use a different empirical strategy and complement their paper by showing that infection risk gives rise to racial animus outside the lab as well. The fact that Covid-19 induces racial animus in both the United States and the Czech Republic suggests that the phenomenon documented in our papers is likely generalizable globally.
Finally, our work speaks to the literature on the role of political rhetoric. Political rhetoric has been shown to influence public opinions and behavior, such as presidential approval (Druckman and Homes, 2004 ) and public perception of a foreign country (Silver, 2016) . In particular, Müller and Schwarz (2019) find that President Trump's tweets about Islam leads to anti-Muslim hate crimes. Our findings add to theirs by showing that the President's tweets also relate to anti-Asian sentiment, implying the generalizability of such a relationship to other racial attitudes.
Animosity between racial groups at an international level could severely hinder global initiatives to tackle the current pandemic and slow the economic recovery. Our results suggest that educating the public about the dissemination of Covid-19 and de-emphasizing the connection between the disease and a particular racial group can be an effective way to curb the current and future racial animus.
We use two measures to proxy for an area's racial animus against Asians ---the percentage of Google searches and Twitter posts that include the word "chink" or "chinks". The c-word is not uncommon in Google searches or in tweets. Between June 2019 and June 2020, the racial epithet was included in over a quarter million Google searches and 60 thousand tweets. 6 This is about the same number of Google searches as the word "democrat" and 3 percent of tweets as the word "economists".
We obtain the data from two sources. First, Google search data are obtained using Google Trends.
We download weekly Google search data for the c-word at the media market level between July 2019 and April 2020. The data are not the raw number of searches, but the weekly percentage of searches including the term over all searches in a media market search rate, scaled by the highest weekly search rate in the same market during the whole time period that one extracts the data for ---in our case, between July 2019 and April 2020. In particular, racially charged Google search index for media market m at time t extracted over period T is approximately:
This metric is able to capture the timing of a change in an area's racially charged search index but not the absolute level of the change. In Appendix A, we re-scale the search index so that the index in different media markets is normalized using the same base. However, doing so leaves us with only 60 percent of the original sample. Therefore, we focus on the timing of the change in the main results and report the results using the re-scaled version in the appendix.
We are able to extract racially charged Google search index for 60 over 210 media markets, covering around 40 percent of the U.S. population in 33 states. We are not able to extract the data for other media markets because Google does not report the data when the search index for a given area and time is below an unreported threshold. Compared to media markets with no racially charged search index, those in our sample have higher population and exhibit a quadratic relationship with the percentage of Asian population but do not differ in other measurable dimensions, such as local unemployment rate or support for democratic versus republican party (Table A1) . 7 Analyses using Google data are done at the media market level.
Second, Twitter data are obtained from Crimson Hexagon, which houses all public tweets through a direct partnership with Twitter. We download all geo-located tweets that include the c-word between November 2019 and April 2020. Crimson Hexagon does not provide data on the total number of tweets posted in a given area and time. We thus extract the number of all public tweets including "the", the most common word on Twitter, to approximate the total Twitter activity in each county on each day. The assumption is that the proportion of tweets including "the" is stable across areas, and the number of tweets including "the" can approximate total activity on Twitter. We define racially charged Twitter post index for a given county and time as the number of tweets that include the c-word per 100,000 tweets including "the".
We have valid Twitter post index in 612 counties across 51 states, encompassing roughly 59.5 percent of the U.S. population. Counties are not in the sample because their residents do not use Twitter, do not disclose geo-identifiers on Twitter, or do not post any tweets including "the" in the sample period. 8 Counties with valid Twitter post index on average have a larger population, more educated residents, and slightly higher support for democratic party than do counties without the data (Table A1 ). Analyses using Twitter data are done at the county level unless noted otherwise.
Admittedly, Google and Twitter data suffer from sample selection either due to low search activities or missing geo-identifiers. But given that areas with Google data and those with Twitter data are not highly correlated (correlation=0.053 at county level), using both data sources can alleviate the concern about the external validity of our findings.
For racially charged Google search index and Twitter post index to be meaningful proxies for racial animus, the only assumption we need is that an increase in racial animus makes one more likely to use the cword. Under this assumption, higher racial animus will result in a higher percentage of Google searches and 7 tweets that include the racial epithet. Existing papers that use a similar proxy for racial animus suggest that the assumption is likely to hold in reality (Anderson et al., 2020; Depetris-Chauvin, 2015; Stephens-Davidowitz, 2014). Common terms in racially charged Google searches and tweets also support the assumption. During our sample period, some most common terms in these searches are "chinked eye" and "chink virus"; common terms in these tweets are phrases like "chink virus", or directly addressing another individual as a "chink". Furthermore, over 67 percent of these tweets are tagged with emotion of "anger" or "disgust". 9 We benchmark our proxies with common measurement of racial animus and consumer discrimination. We begin by presenting the relationship between the proxies and anti-Asian hate crimes.
Hate crime data come from the FBI Uniform Crime Reports (UCR) Hate Crime Statistics and are available up to 2018. 10 A majority of these hate crimes are personal crimes, including simple or aggravated assault (30 percent) and in-person intimidation (34 percent). Table 1 The relationship between racially charged search index and hate crimes is mainly contemporaneous as the coefficient on the last month's search index is small and insignificant.
Next, we change the dependent variable to monthly visits to Chinese restaurants in the local area between January 2018 and December 2019. Restaurant visit data are from Safegraph and available starting in 2018. 11 As shown in Table 1 panel A columns (7) and (8), a one standard deviation increase in racially charged search index links to roughly 160 to 190 fewer visits to Chinese restaurants per one million population in each media market each month, controlling for media market and year month fixed effects as well as search index for "Asian(s)". This decrease equals to about 0.6 to 0.7 percent of the average monthly visit rate. The relationship between search index and visit rate is also mainly contemporaneous.
We replicate the above correlations using Twitter data in Table 1 panel B. We aggregate hate crimes to the media market level due to low occurrence at the county level. To maintain consistency, we also aggregate restaurant visits to the media market level. Overall, racially charged Twitter post index does not 9 Crimson Hexagon assigns each tweet one or more emotion tag(s) generated via natural language processing algorithm. The algorithms can distinguish the difference in emotions between tweets even when the words included are similar, for instance, the difference between "I want a burrito so bad" and "I just had a burrito. It was so bad.". For a detailed description, please refer to https://www.brandwatch.com/blog/understanding-sentiment-analysis. 10 Over 80 percent of the U.S. population is covered by police agencies that voluntarily report hate crime data to UCR (Ryan and Leeson, 2011). 11 Safegraph partners with mobile applications and collects anonymous user location data to calculate the foot traffic to around 4.1 million points of interest in the United States.
correlate with anti-Asian hate crimes or visits to Chinese restaurants. One potential explanation is that Twitter data represent the public display of racial animus and undergo higher social censoring. We may only see a change on Twitter when the shift in racial animus is substantially large.
Our empirical strategy relies on the plausibly exogenous variation in the timing of the first Covid-19 diagnosis across regions in the United States. We download the data on all Covid-19 cases and deaths in the United States between Jan 21st and April 26th, 2020 from John Hopkins University Covronavirus
Resource Center. We match the date of the first Covid-19 diagnosis in each county and media market to those with valid Google and Twitter data. All media markets have their first diagnosis in the sample period and have at least six weeks after the first diagnosis. We exclude seven counties that do not have diagnoses in the sample period and 18 counties whose first diagnosis is after March 29th 2020 to ensure that all counties have at least four weeks after the first diagnosis. The remaining counties and media markets constitute our main regression sample. The county-and media-market-level predictors of being in the main sample are presented in Table A1 . Figure Table A2 . Areas with higher population and more males tend to have their first cases earlier but, interestingly, areas with more Asians do not.
In Figure 1 
Our main strategy is a difference-in-differences event study where the first Covid-19 diagnosis in a county or a media market is the event of interest. The specification is as follows:
where is racially charged Google search index or Twitter post index in county or media market in
week . is the week when has its first Covid-19 diagnosis. refers to event dummies indicating the number of weeks before or after the first local diagnosis. We omit the dummy for the week before the first diagnosis due to perfect collinearity. We include six weeks of post-period for Google data and four weeks for Twitter data because longer post-period will result in unbalanced sample in event time. is a vector of area-specific controls such as the number of diagnoses or deaths related to Covid-19, an indicator for state-level stay-at-home order, and search index or post index for "Asian(s)". We is inherently untestable, but we can assess its plausibility by testing for parallel pre-trends. We provide evidence that the assumption is likely to hold in the next section.
We start by examining how an area's search of the c-word on Google respond to the first local Covid-19 diagnosis. Figure 2 panel A plots the estimates of the coefficients on the event dummies from regression 2 using an area's racially charged Google search index as the outcome. The search index reaches the peak in the week after the first local diagnosis and decreases slightly in later weeks. We also present the estimates using the search index scaled by the same maximum of Fresno-Visalia in California in Figure A3 as a robustness check. This is because the estimates using the original search index do not map to an increase over a national base, as the maximum search rate is different across areas. The overall pattern is similar whether we use the rescaled or the original index, but the magnitude of the former is about one-third to two-thirds of the latter because the maximum of Fresno-Visalia is larger than that of most media markets. The confidence intervals are also larger because 40 percent of the sample are lost when we re-scale. 15 To better interpret the effects and understand how public expression of the c-word changes, we turn our attention to Twitter. Similar to Google search index, racially charged Twitter index also peaks in the week after the first local Covid-19 diagnosis and slowly decreases afterwards, as plotted in Figure 2 panel B. Table A4 panel B further shows that, relative to the week before the first diagnosis, racially charged tweets increase by 1 and 0.6 per 100,000 "the" tweets in the first and second week after the first diagnosis. The increase amounts to roughly 100 and 66 percent of the outcome mean. In columns (2) through (4) in in Table A3 and A4, we control for the number of confirmed cases and deaths, whether a state-level stay-at-home order is in place, general interest in terms like "Asian(s)", and excluding earlyand hard-hit state, such as New York, Washington, and California. The estimated effects increase slightly after controlling for the covariates.
To get at the exact timing when the usage of the c-word starts to change, we run regression 2 using the daily search and post index as outcomes, additionally controlling for day-of-week fixed effects.
Regression estimates are plotted in Figure A4 . The effects start to appear around two to three days after the first local diagnosis. The local residents indeed pay attention to the Covid-19 situation in their neighborhood and respond quickly to the first diagnosis.
One may concern that the increase in the usage of the c-word is driven by reasons other than higher animosity against Asians, such as an increase in online activities due to blanket stay-at-home orders, a rise in benign attention to China or Asia, seasonality in racist online activities, or "Twitter bots".
These factors are unlikely to explain our findings. First, the search and the post index are normalized by the total searches or tweets in a given area and time and thus already account for overall change in online activities. Second, Table A3 column (3) shows that our results are robust to controlling for the search and the post index for terms which capture general attention to China or Asia but are neutral in connotation, such as "Asian(s)", "China", or "Asia". 16 Third, to test the seasonality in racist online activities, we generate a "fake" Covid-19 diagnosis date for each area using the same calendar day and month of its actual diagnosis date but change the year to 2019. Reassuringly, we find no increase in racially charged search and post index surrounding the "fake" dates, as shown in Figure A5 . Finally, some may worry that "Twitter bots" rather than local residents contribute to the increase in racially charged tweets. Twitter proactively identifies and removes automation generated content which can alleviate this concern to some extent (Roth and Pickles, 2020). In addition, our results do not quantitatively change when we drop frequent c-word users who are subject to suspicion of to be bots, defined as those who used the epithet more than five times (99 percentile) during the sample period. Results are available upon request.
So far, we have shown that the Covid-19 pandemic raises both individuals' hidden animosity against Asians and their public display of the animosity. A natural next question is who contributes to the rise. Do more individuals start to harbor the animus or do a few existing racists increase their animosity?
Taking advantage of unique Twitter user identifiers, we can breakdown the increase in racially charged tweets by whether their authors are first-time or existing c-word users. We define existing c-word users as those who tweeted the c-word at least once between 2014 and the sixth week before the first local Covid-19 diagnosis. We define new c-word users as those who never tweeted the c-word between 2014 and the sixth week before the first local diagnosis and who had at least 10 tweets before their first c-word tweets.
Importantly, this definition can avoid counting newly registered Twitter users as new c-word users. Figure   3 plots the breakdown. The increase in racially charged tweets is mainly driven by new c-word users rather than pre-existing ones. This breakdown suggests that the Covid-19 pandemic induces more existing 
In this section, we discuss several non-mutuality exclusive explanations as why the Covid-19
pandemic spurs animosity against Asians.
Fear of infectious diseases. Evolutionary psychologists have long argued that desire to avoid harmful communicable diseases contributes to contemporary prejudices against subjective outgroups (Schaller and Neuberg, 2012) . Lab experiments also show that xenophobia toward unfamiliar immigrant groups is stronger when the threat of infectious diseases is more salient (Faulkner et al., 2004) . Moreover, surveys administered in March and April 2020 document that around 60 to 80 percent of Americans are worried about contracting Covid-19, suggesting that fear of the disease indeed exists among the locals (Binder, 2020; Saad, 2020) . In our main analysis, we also show that local racial animus responds to a salient increases of infection risk.
and the Asian population could also play a key role in fueling the animosity against Asians. First, if the salient connection is not a main driving force, the disease-avoidance theory would predict rising animus against all minorities, not just Asians. We construct Google search index and Twitter post index for common racial epithets against major minority groups in the United States, such as "nigger(s)" against African Americans, "wetback(s)" against Hispanics, and "kike(s)" against the Jewish population. 17 We run regression 2 using racially charged searches and tweets against other minorities as outcomes. We include an indicator for the week of January 26 2020 when using the n-word as the outcome, because
Kobe Bryant's death together with MSNBC Anchor using the n-word when broadcasting the news of the death leads to a spike in its use. We also include an indicator for the week of February 23 2020 when using the k-word as the outcome, because Los Angeles Dodges player Enrique ("Kiké") Hernandez's performance in that week leads to spike in the use of the k-word. Coefficients on the event dummies are plotted in Figure A6 . None of the examined racial epithets experience increase in Google searches following the first local diagnosis; if anything, searches for the n-word see a slight decrease. Similar pattern is found for the w-word and the k-word on Twitter. 18 These findings suggest that the connection 17 We do not use "spic(s)" as the racial epithet against Hispanics, because the term is included in "Spic and Span", the name of an all-purpose household cleaner brand, which experienced growing interest since the start of the Covid-19 outbreak. Breakout Google queries and a substantial number of tweets including the term are about the brand and not the slur. In addition, we do not include "redskin(s)", a common racial epithet against Native Americans, because the term is included in the name of a professional American football team "The Washington Redskins". Google queries and tweets including the term are mostly about the football team, such as, "chase young redskins" and "redskins draft". 18 We present Twitter post index for the n-word separately in Figure A7 due to the seasonality in the use of the nword on Twitter. The seasonality is evident when comparing the n-word usage between 2019 and 2020 in panel A. The seasonality may arise from a combination of Black History Month taking place in February and the n-word being reclaimed by African Americans (Croom 2011 We define an area to be more (less) susceptible to the negative impact if the proportion of the area's annual average employment in "Leisure and Hospitality" and "Education and Health Services", the two hardest-hit industries in employment according to Bureau of Labor Statistics, is above (below) the sample median (i.e., 32 percent in the Google sample and 35 percent in the Twitter sample). Figure A9 because a video tweet unrelated to Covid-19 but with n-word in the description went extremely viral on February 10th and contributed to 95 percent of the n-word tweets on that day. 19 We define a tweet to be related to China if it contains any of "China", "Chinese", "Huawei", or "Xi" and a tweet to be related to Covid-19 if it contains any of "covid", "covid-19", "corona", "coronavirus", "virus", "epidemic", or "pandemic". Table A5 presents examples of Trump's tweets in each category, and Figure A8 plots the daily frequency of such tweets. We only include data after January 1st 2020 because Trump did not tweet about Covid-19 until late January 2020.
shows areas experiencing high versus low negative economic impact do not respond differently to the first local Covid-19 diagnosis. One potential reason is that the impact of the pandemic on local economy was not well understood at the onset of the first Covid-19 diagnosis. According to surveys administered in early March and April 2020 (Binder, 2020 ; Saad, 2020), Americans were more worried about the effect of Covid-19 on their health than on their personal finances.
Taken together, our findings imply that the pressing infection risk and the salience of the connection between the disease and the Asian population play a bigger part than future economic impact in motivating the initial racial animus.
In this paper, we estimate the effect of the Covid-19 pandemic on racial animus, as measured by
Google searches and Twitter posts including the c-word. Our main finding is that the Covid-19 pandemic sparks racial animus against Asians. Shortly after the first Covid-19 diagnosis in an area, the locals start to search for and tweet the c-word more often. Fear of contracting Covid-19 and the salient connection between the disease and the Asian population is a main driving force for the rising animosity against
Asians. This increase could indicate a rise in future hate crimes, as we document a strong correlation between the use of the slur and anti-Asian hate crimes using historic data. Moreover, the rise in racially Animosity between racial groups could severely hinder global initiatives to tackle the current pandemic and slow economic recovery. Our results suggest that educating the public about the dissemination of Covid-19 and de-emphasizing the connection between the disease and a particular racial group can be an effective way to curb the current and future racial animus.