We are two physicians whose clinical work and research focuses on the social causes of health and disease. In particular, we’ve seen firsthand how housing instability influences health outcomes.
Homelessness takes many forms, including living on the street or in a car, motel or shelter, or staying temporarily with friends or family. This last scenario is known as “doubling up.”
Our findings suggest that 1 in 4 Denver youth age 14 to 17 experienced some form of homelessness in 2021, and that the number of youth experiencing homelessness in Denver is many times greater than what traditional methods find.
In our study, we used three data sources in what’s known as a multiple systems estimation approach. This approach has been used to count other difficult-to-measure groups of people, including those with substance use disorders or COVID-19. Rarely has it been applied to homelessness.
We combined these datasets to avoid overlap between individuals and counted unique youth present in the data. We then used statistical modeling techniques to estimate those who are “unknown” – meaning not identified in the data. Together, these combined known counts and “unknown” estimates can give a more complete size of the total population.
Among our findings, we noted that 75% to 83% of youth experiencing homelessness in Denver identified as Black/African American or Hispanic.
To count people experiencing homelessness, states and homelessness service providers most often rely on point-in-time counts. In a point-in-time count, local service providers interview and record people experiencing homelessness on one night in January of each year. Typically, only people who are living on the streets or in shelters are counted.
In January of each year, local service providers record people experiencing homelessness. Boston Globe/GettyImages
Point-in-time counts are crucial for policy decisions around homelessness because they help local, state and national organizations and governments allocate resources.
However, point-in-time counts may miss people living in motels, doubling up, those who experience homelessness at other times of the year beyond January, and others. Consequently, many experts and researchers recognize that these counts give incomplete data.
Service providers and governments need new methods to count those experiencing homelessness. From Denver to Washington D.C., they cannot appropriately make decisions or adequately fund evidence-based interventions using incomplete numbers. We believe our methods can be an important piece of the toolbox to improve estimates and better inform policy.
What’s next
Even according to traditional point-in-time counts, homelessness continues to rise significantly across Colorado and nationally. Our results suggest many more youth, and likely persons from all walks of life, are experiencing homelessness than previously known.
Our team is working to use this methodology at the state level in Colorado. We plan to expand our counts to include adults in order to improve estimates among racial and ethnic minorities, LGBTQ+ people and other at-risk communities.
At the same time, our results demonstrate that multiple systems estimation can be an important tool in Colorado and nationally. Our team is optimistic that other researchers, service providers and governments will begin to use this method in their localities.
We hope that with a better understanding of the scope of homelessness, legislators and service providers can implement more effective policies to address this hidden crisis.
The Research Brief is a short take on interesting academic work.
The U.S. officially imposed new 25% tariffs on Canada and Mexico on March 4, 2025, following through on a long-delayed pledge from President Donald Trump. American consumers and businesses are now bracing for higher costs and potential supply disruptions.
Although tariffs, or taxes on imports, are a pillar of Trump’s economic policy, the move still surprised many observers, since Mexico and Canada are among the U.S.’s traditional allies and top trading partners. The administration further rattled global supply chains by doubling existing tariffs on Chinese goods to 20%.
As an economist who studies global trade, I wanted to know how the 25% import duties on Canada and Mexico would affect different parts of the country. So I conducted a state-by-state impact analysis.
What I found is alarming: The U.S. economy could face an annual loss of US$109.23 billion. This shortfall would mean rising costs of everyday goods for American families and would disproportionately affect certain states. My analysis focused exclusively on the effects of U.S. tariffs, so it didn’t take retaliation from Canadaor Mexico into account. If it did, the losses would be even greater.
Unequal burdens for states, higher prices for families
Imagine your grocery bill surging by 17.5% to 25%, car parts costing hundreds of dollars more, and your favorite local restaurant raising prices as imported ingredients become unaffordable. Because tariffs drive up consumer prices, these scenarios, or others like them, will soon become reality across the U.S.
But not all Americans will be affected equally, I found. States that are deeply connected to North American supply chains will suffer the biggest economic blows. Texas, with its strong trade ties to Mexico and key role in energy, would lose $15.3 billion. California’s diverse economy would take a $10.2 billion hit. Michigan, heavily reliant on auto manufacturing, would face a $6.2 billion blow – over 1% of its gross domestic product.
The biggest losers from the policy on a per-capita basis would be smaller, trade-dependent states that lack the flexibility to absorb such a shock. New Mexico, Kentucky and Indiana would be among the hardest hit, with projected GDP losses ranging from 1.12% to 1.48%. These states rely heavily on manufacturing and specialized industries, making them particularly vulnerable to rising costs and supply chain disruptions.
Take New Mexico. While it may not experience the largest total economic loss, it would bear the highest per-person burden. That $1.73 billion hit to its economy would translate to $822 for every resident – a devastating blow in a state where incomes are already below the national average.
Indeed, the likely effects of tariffs will be felt especially hard by American families. For example, a family of four in New Mexico would see an estimated $3,288 additional annual costs, equivalent to three months of grocery bills or an entire year’s utility expenses. Families in Kentucky and Indiana would also bear heavy financial burdens, paying an extra $3,120 and $2,836, respectively. Even in wealthier states such as Texas, the added annual costs would reach over $2,000 per household.
For middle- and lower-income families, these aren’t trivial costs. They represent difficult trade-offs, forcing households to cut back on essentials, delay major purchases or dip into savings to make ends meet.
A truck crosses the Ambassador Bridge, a border crossing between Windsor, Ontario, Canada, and Detroit, Mich., on March 1, 2025. Geoff Robins/AFP via Getty Images
Where industry will face a tough hit
Perhaps no industry would suffer more than the auto sector, particularly in states such as Michigan, Indiana and Kentucky. These regions rely on a highly integrated North American supply chain, where components cross borders multiple times before a final product reaches consumers. Tariffs would disrupt this delicate balance, leading to price increases, reduced production and job losses.
My conservative estimate shows that such disruptions could cost the industry approximately $28.2 billion, putting around 680,000 jobs at risk across manufacturing, parts production and sales operations. And the ripple effects would extend beyond automakers to suppliers, dealerships and local economies.
But the pain wouldn’t stop there. Manufacturing, which plays a critical role in 17 of the top 20 states most affected by tariffs, would also face rising costs and shrinking profit margins. The agricultural sector – vital in at least 10 states – would endure higher input costs and potential retaliatory tariffs from Mexico and Canada. Past trade disputes have shown that American farmers often bear the brunt of such policies, with lost export markets and declining revenues.
During the U.S.-China trade war of 2018-2019, for example, American farmers suffered over $27 billion in losses, with soybean exports dropping by 71% and states such as Iowa, Illinois and Kansas losing billions in GDP. The federal government paid affected farmers more than $23 billion to offset these losses. Similar – and possibly worse – challenges loom now.
Retaliation from Mexico and Canada could deal a heavy blow to agricultural exports – including corn, beef and dairy – that anchor local economies, especially in Iowa, Nebraska and Wisconsin. Both countries have threatened countermeasures targeting key U.S. exports, raising concerns among farmers and agribusinesses. Retaliatory tariffs could shrink profit margins, further disrupt supply chains, and create uncertainty for producers relying on these markets.
Looking at the bigger picture
The new Trump tariff regime represents a fundamental shift in how the U.S. engages with its closest economic partners. While ostensibly meant to strengthen American industry, the tariffs on offer have serious side effects that will likely cause widespread disruptions for businesses, consumers and entire state economies.
Trade isn’t just about numbers on a spreadsheet. It’s about real people, real businesses and the intricate economic fabric that connects the nation. Changes to this system can come at a high price. Safeguarding American jobs and ensuring economic stability entails recognizing the realities of global trade and considering the trade-offs of instituting new policies.
While tariffs are one method of disrupting the status quo, they are far from the only way. Indeed, reform is also possible through targeted policies – including negotiated trade agreements, investment incentives and workforce development programs – that address trade concerns without altering deeply integrated supply chains.
What if extreme heat not only leaves you feeling exhausted but actually makes you age faster?
Scientists already know that extreme heat increases the risk of heat stroke, cardiovascular disease, kidney dysfunction and even death. I see these effects often in my work as a researcher studying how environmental stressors influence the aging process. But until now, little research has explored how heat affects biological aging: the gradual deterioration of cells and tissues that increases the risk of age-related diseases.
New research my team and I published in the journal Science Advances suggests that long-term exposure to extreme heat may speed up biological aging at the molecular level, raising concerns about the long-term health risks posed by a warming climate.
My colleagues and I examined blood samples from over 3,600 older adults across the United States. We measured their biological age using epigenetic clocks, which capture DNA modification patterns – methylation – that change with age.
DNA methylation refers to chemical modifications to DNA that act like switches to turn genes on and off. Environmental factors can influence these switches and change how genes function, affecting aging and disease risk over time. Measuring these changes through epigenetic clocks can strongly predict age-related disease risk and lifespan.
Research in animal models has shown that extreme heat can trigger what’s known as a maladaptive epigenetic memory, or lasting changes in DNA methylation patterns. Studies indicate that a single episode of extreme heat stress can cause long-term shifts in DNA methylation across different tissue types in mice. To test the effects of heat stress on people, we linked epigenetic clock data to climate records to assess whether people living in hotter environments exhibited faster biological aging.
We found that older adults residing in areas with frequent very hot days showed significantly faster epigenetic aging compared with those living in cooler regions. For example, participants living in locations with at least 140 extreme heat days per year – classified as days when the heat index exceeded 90 degrees Fahrenheit (32.33 degrees Celcius) – experienced up to 14 months of additional biological aging compared with those in areas with fewer than 10 such days annually.
This link between biological age and extreme heat remained even after accounting for a wide range of individual and community factors such as physical activity levels and socioeconomic status. This means that even among people with similar lifestyles, those living in hotter environments may still be aging faster at the biological level.
Even more surprising was the magnitude of the effect – extreme heat has a comparable impact on speeding up aging as smoking and heavy alcohol consumption. This suggests that heat exposure may be silently accelerating aging, at a level on par with other major known environmental and lifestyle stressors.
Long-term public health consequences
While our study sheds light on the connection between heat and biological aging, many unanswered questions remain. It’s important to clarify that our findings don’t mean every additional year in extreme heat translates directly to 14 extra months of biological aging. Instead, our research reflects population-level differences between groups based on their local heat exposure. In other words, we took a snapshot of whole populations at a moment in time; it wasn’t designed to look at effects on individual people.
Our study also doesn’t fully capture all the wayspeople mightprotect themselves from extreme heat. Factors such as access to air conditioning, time spent outdoors and occupational exposure all play a role in shaping personal heat exposure and its effects. Some individuals may be more resilient, while others may face greater risks due to preexisting health conditions or socioeconomic barriers. This is an area where more research is needed.
What is clear, however, is that extreme heat is more than just an immediate health hazard – it may be silently accelerating the aging process, with long-term consequences for public health.
Large swaths of the U.S. population are experiencing long stretches of extreme heat, as this map of cumulative heat days from 2010 to 2016 shows. Eunyoung Choi, CC BY-ND
Older adults are especially vulnerable because aging reduces the body’s ability to regulate temperature effectively. Many older individuals also take medications such as beta-blockers and diuretics that can impair their heat tolerance, making it even harder for their bodies to cope with high temperatures. So even moderately hot days, such as those reaching 80 degrees Fahrenheit (26.67 degrees Celcius), can pose health risks for older adults.
As the U.S. population rapidly ages and climate change intensifies heat waves worldwide, I believe simply telling people to move to cooler regions isn’t realistic. Developing age-appropriate solutions that allow older adults to safely remain in their communities and protect the most vulnerable populations could help address the hidden yet significant effects of extreme heat.
Gifts from top 50 US philanthropists rebounded to $16B in 2024 − Mike Bloomberg; Reed Hastings and Patty Quillin; and Michael and Susan Dell lead the list of biggest givers
The 50 American individuals and couples who gave or pledged the most to charity in 2024 committed US$16.2 billion to foundations, universities, hospitals and more. That total was 33% above an inflation-adjusted $12.2 billion in 2023, according to the Chronicle of Philanthropy’s latest annual tally of these donations. Media mogul and former New York City Mayor Mike Bloomberg led the list, followed by Netflix co-founder and chairman Reed Hastings, along with his wife, Patty Quillin. Businessman Michael Dell and his wife, Susan Dell, pledged the third most in 2024.
Neither MacKenzie Scott nor Elon Musk, both of whom announced donations large enough to land them on this list, provided enough information for the Chronicle to include them. Musk didn’t name the nonprofits to which he gave stock, and Scott declined to confirm how much money she put into the donor-advised funds through which she gives. Known as DAFs, these funds are savings accounts reserved for charitable giving.
The Conversation U.S. asked David Campbell, Lindsey McDougle and Susan Appe, three philanthropy scholars, to assess the significance of these gifts and to consider what they indicate about the state of charitable giving in the United States.
What trends stand out overall?
Appe: I think it’s good to see that eBay founder Pierre Omidyar, an Iranian-American entrepreneur born in France, with his wife Pam, are among the top 12 donors. Omidyar is the only foreign-born philanthropist on this list who reported giving to democracy promotion in the U.S. through his Democracy Fund. The Omidyars also funded the AI Collaborative, a group that promotes artificial intelligence governance based on democratic values, and their Omidyar Network, an organization promoting responsible technology.
Omidyar is one of seven immigrants among 2024’s top U.S. donors. The others are Herta Amir, who was born in what was then Czechoslovakia; Sergey Brin, a Russian immigrant; the Pagidipati family, which came from India; K. Lisa Yang, who was born in Singapore; Michele Kang, who immigrated from South Korea; and Joe Wen, a Taiwanese immigrant.
In 2024, as in most years, many of these wealthy donors supported prestigious universities and large hospitals and stowed millions in their own foundations and donor-advised funds. Although it’s impossible to predict exactly what their foundations and DAFs will support in the future, history suggests that they’re unlikely to focus on addressing systemic issues such as economic inequality.
McDougle: It doesn’t appear that any of these top 50 donors are Black or Latino. This lack of representation is undoubtedly a reflection of broader societal disparities and may influence how individuals from these groups perceive their own potential as philanthropists.
Philanthropic capacity often correlates with wealth accumulation, and significant gaps in wealth between racial groups are likely to have a direct influence on who we see in the Philanthropy 50. Black families, for instance, possess just 15% of the wealth of white families, while Hispanic families have only about 22%. These wealth disparities likely prevent many Black and Latino Americans from having the wealth necessary to engage in large-scale philanthropy.
This reality highlights the need for the nation’s leading philanthropists to fund initiatives that focus on addressing systemic barriers to economic equality. MacKenzie Scott has been doing this through the millions of dollars she has donated to support racial equity and economic mobility.
Addressing these disparities also involves changing the narrative around who is considered a philanthropist. As I have argued before, underrepresented groups may not always see themselves as philanthropists, partly due to limited resources and the historical portrayal of philanthropy as the domain of the wealthy. But by redefining philanthropy to include a broader spectrum of giving, philanthropy can play a pivotal role in leveling the playing field and creating more opportunities for all.
What surprises you about the biggest donors?
Appe: The absence of Oracle co-founder Larry Ellison, Google co-founder Larry Page and former Microsoft CEO Steve Ballmer also stands out due to the presence of many other tech billionaires, including Mark Zuckerberg and Bill Gates, on this list.
Campbell: In addition to Elon Musk, a South African immigrant, not making this list for the second year in a row – even though he is the richest person in the world – Jeff Bezos isn’t listed either. Few private citizens have sought to change American society more than they have – Musk most recently through his role in the so-called Department of Government Efficiency and Bezos through actions he takes as the owner of The Washington Post and the founder of Amazon, among other initiatives.
I believe that it is worth asking why neither of these men, who rank among the wealthiest Americans, made the list this year. While Musk gave too little information to make the list, his previous giving choices raise questions about his commitment to philanthropy as a way to advance the public good. In 2022 and 2023, for example, his foundation gave away less money than required by law and supported organizations that benefit him and his interests, such as schools attended by his children.
Do you have concerns about the big gifts these donors provide?
McDougle: The nonprofits receiving these large donations can end up in a precarious situation if that funding suddenly stops. When nonprofits rely too heavily on a few wealthy donors, they may be forced to make abrupt decisions like cutting crucial programs or laying off staff. Obviously, this underscores a core problem with overdependence on these types of major gifts: They can leave nonprofits in a bind and unable to sustain their operations without continued long-term support.
This is particularly problematic if it affects a nonprofit’s ability to engage in long-term planning. As such, when focusing on the giving of the super rich, it is important to consider not just the immediate benefits of their generosity but also the potential instability it can create for the recipients if their gift is not managed strategically.
Campbell: The total given by America’s top donors in 2024 was the sixth-highest in the past decade, after adjusting for inflation. I’d expected to see a larger amount, given that 2024 was the second straight year of stock market gains of 20% or more.
In 2020, when the COVID-19 pandemic began, the top donors gave nearly twice as much to charity as they did this past year; and they gave close to $8 billion more than that in 2021. Why haven’t the wealthiest Americans sustained that level?
Giant gifts to universities, museums and hospitals are surely making a meaningful difference in America and the world. But I wonder why these donors tend not to focus on the challenges facing those who have the least.
To be sure, some of these philanthropists use the foundations they or their relatives control to help meet the basic needs of Americans struggling to get by and address issues such as poverty, disease prevention and criminal justice reform. Melinda French Gates, Warren Buffett, and John and Laura Arnold all directed much of their giving in 2024 to those kinds of foundations.
What do you expect or hope to see in 2025 and beyond?
Top philanthropists have been slow to react so far. However, the MacArthur Foundation just announced plans to increase its giving over the next two years. MacArthur president John Palfrey said this is a response to what he called a “major crisis” brought on by the Trump administration’s spending cuts. I will observe whether other foundations or some of the wealthiest Americans follow suit.
Still, philanthropy cannot fill all these gaps. The $60 billion in foreign aid cuts represent a sliver of the trillions the Trump administration wants to slice from the federal budget. If it succeeds, donors will have countless other priorities.
Campbell: Events that took place during the first Trump administration, like the murder of George Floyd, the erosion of democratic norms and the separation of immigrant families, led philanthropists to embrace giving that addressed these issues, notably diversity, equity and inclusion initiatives. In the early days of the second Trump administration, prominent donors like Mark Zuckerberg have enthusiastically backtracked on their own DEI policies. I am now watching how other donors position themselves relative to the Trump administration’s objectives – as cheerleaders, combatants or something in between.
The Bill & Melinda Gates Foundation and Arnold Ventures have provided funding for The Conversation U.S. in the past. The Gates foundation currently provides funding for The Conversation internationally.
