Tian Gan
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Doctoral Track Student
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Mechanical and Aerospace Engineering
Dissertation/Research Advisor: Maurizio Porfiri
My research focuses on developing network and graph-based models of complex urban systems. I am currently working on developing a multidimensional model describing the interactions between doctors and patients. Our research will help increase the equitable distribution of medical care in cities and inform decision-making in public health.
Research News
New York City's medical specialist advantage may be an illusion, new NYU Tandon research shows
New York City offers nearly every type of medical specialist but provides fewer specialty healthcare providers per capita than smaller cities, according to a new study that challenges conventional assumptions about urban healthcare advantages and reveals a troubling paradox across America's largest metropolitan areas.
The research, published in Nature Cities, analyzed data from 1.4 million healthcare providers across 75 medical specialties in 898 metropolitan and micropolitan areas. The innovative approach combines urban scaling theory—which examines how city characteristics change with population size—with network science and economic geography to examine healthcare access in unprecedented detail.
Rather than treating healthcare as a single entity, the researchers examined each medical specialty separately, revealing that 88% exhibit what they call "sublinear scaling," meaning larger cities have proportionally fewer specialists per resident than smaller ones.
"We're discovering that the healthcare advantages of living in big cities may be an illusion when it comes to specialized care," explains lead researcher Maurizio Porfiri. "We all assume residents of large metropolitan areas have better access to healthcare than residents of smaller cities, but this is really true only for primary care services. Our findings suggest this assumption breaks down completely for medical specialists. A small city may not offer all the specialties of large cities, but in what it offers it may outperform them.”
Porfiri is an NYU Tandon Institute Professor with appointments in the Departments of Mechanical and Aerospace Engineering (MAE), Biomedical Engineering (BME), Civil and Urban Engineering (CUE), and Technology Management and Innovation (TMI). He also serves as Director of the NYU Center for Urban Science + Progress (CUSP).
The study represents the latest application of Porfiri's urban scaling methodology, which he has previously used to analyze gun violence patterns and the relationship between city living, ADHD and obesity. His research uses Scale-Adjusted Metropolitan Indicators (SAMIs) to control for population differences and reveal how cities deviate from expected patterns.
The study found that while cities like New York and Chicago offer nearly all examined specialties (NYC has 74 — missing only anesthesiology assistants — and Chicago has all 75), residents may face longer wait times and specialists higher patient loading.
In contrast, smaller cities may lack certain specialties entirely—73 of the 75 specialties showed significant associations between availability and population size—but those that exist serve fewer patients per provider. For example, Marshfield, Wisconsin provides 16.8 specialists per 1,000 residents compared to New York's 4.7 per 1,000.
Among the most underrepresented specialties in large cities per capita are addiction medicine, preventive medicine, osteopathic manipulative medicine, and micrographic dermatologic surgery.
Addiction medicine shows the starkest disparity, with large cities providing dramatically fewer specialists per resident than smaller areas. These fields showed the strongest sublinear scaling, meaning residents of major metropolitan areas have significantly fewer of these specialists available relative to their population size compared to smaller cities.
The research identifies two mechanisms driving this paradox: higher patient loads overwhelming specialists in large cities, and economic clustering that concentrates medical expertise in dense hospital networks, creating geographic inequalities.
“The findings have serious implications as the U.S. population ages. The study found sublinear scaling in geriatric specialties like urology and gerontology, suggesting major metropolitan areas may be unprepared for growing elderly populations,” said Tian Gan, a NYU Tandon mechanical engineering PhD student in the urban science track, and the paper’s lead author.
Geographic patterns reveal stark regional disparities. The highest specialist concentrations cluster in the Midwest—Minnesota alone claims two of the top five cities—while all five cities with the lowest access are in the South.
Not all specialties follow this pattern. Several key specialties—including anesthesiology, internal medicine, and clinical psychology—actually have more providers per capita in large cities, reflecting higher urban demand for these services.
The research provides a framework for understanding healthcare distribution that moves beyond the traditional urban-rural dichotomy. Rather than viewing cities as uniformly advantaged, policymakers must consider the complex interplay between diversity and provision of medical services.
Along with Porfiri and Gan, the paper's additional author is Tanisha Dighe, NYU Tandon MS student in applied urban science and information. The study was supported by National Science Foundation grants.
APPENDIX: Medical Specialist Availability by City
CITIES WITH THE MOST MEDICAL SPECIALISTS (Cities offering all specialty types)
- Chicago-Naperville-Elgin, IL-IN: 75 specialties
- Houstone-Pasadena-The Woodlands, TX: 75 specialties
- Atlanta-Sandy Springs-Roswell, GA: 75 specialties
- Washington-Arlington-Alexandria, DC-VA-MD-WV: 75 specialties
- Miami-Fort Lauderdale-West Palm Beach, FL: 75 specialties
CITIES WITH THE FEWEST MEDICAL SPECIALISTS (Fewest specialty types available)
- Monroe, LA: 5 specialties
- Zapata, TX: 6 specialties
- Raymondville, TX: 6 specialties
- Synder, TX: 11 specialties
- Andrews, TX: 11 specialties
CITIES WITH THE HIGHEST CONCENTRATION OF SPECIALISTS OVERALL (All non-primary-care specialists combined per 1,000 residents)
- Rochester, Minnesota: 21.1 specialists (home to Mayo Clinic)
- Marshfield, Wisconsin: 16.8 specialists
- Sunbury, Pennsylvania: 16.3 specialists
- Easton, Maryland: 15.7 specialists
- Albert Lea, Minnesota: 15.4 specialists
CITIES WITH THE LOWEST CONCENTRATION OF SPECIALISTS OVERALL (Fewest specialists per 1,000 residents)
- Monroe, Louisiana: 0.1 specialists
- Virginia Beach-Norfolk, Virginia: 0.4 specialists
- Danville, Virginia: 0.8 specialists
- Rio Grande City-Roma, Texas: 1.0 specialists
- Bonham, Texas: 1.0 specialists
SPECIALTIES MOST UNDERREPRESENTED IN MAJOR METROS, 1M+ POPULATION
(Scaling exponents - how fast they grow with population growth )
- Addiction Medicine (0.305) - Most underrepresented
- Preventive Medicine (0.331)
- Osteopathic Manipulative Medicine (0.351)
- Micrographic Dermatologic Surgery (0.379)
- Maxillofacial Surgery (0.398)
- Marriage and Family Therapist (0.400)
- Nuclear Medicine (0.408)
- Advanced Heart Failure and Transplant Cardiology (0.446)
- Certified Clinical Nurse Specialist (0.457)
- Sleep Medicine (0.457)
SPECIALTIES MOST OVERREPRESENTED IN MAJOR METROS
(Scaling exponents - - how fast they grow with population growth)
- Anesthesiology (1.154) - Most overrepresented
- Internal Medicine (1.100)
- Physical Therapy (1.089)
- Clinical Psychology (1.069)
- Physician Assistant (1.057)
- Obstetrics/Gynecology (1.050)
- Neurology (1.039)
- Psychiatry (1.031)
- Gastroenterology (1.022)
NYC SPECIALIST COUNTS (74 out of 75 research specialties)
Missing only: Anesthesiology Assistant
Top 10:
- Nurse Practitioner: 8,977
- Internal Medicine: 8,194
- Physical Therapy: 7,515
- Physician Assistant: 6,224
- Clinical Social Worker: 4,842
- Anesthesiology: 3,637
- Family Practice: 3,259
- Diagnostic Radiology: 2,843
- Emergency Medicine: 2,545
- Psychiatry: 2,465
Notable underrepresented specialties (bottom 5):
- Maxillofacial Surgery: 40
- Micrographic Dermatologic Surgery: 25
- Preventive Medicine: 21
- Marriage and Family Therapist: 18
- Addiction Medicine: 16
Gan, T., Dighe, T. & Porfiri, M. Trade-off between diversity and provision of specialized healthcare in US cities. Nat Cities (2025).
Sophisticated data analysis uncovers how city living disrupts ADHD's path to obesity
A hidden link between impulsivity and obesity may not be fixed in human biology but shaped by the cities we live in.
Using a novel engineering-based approach, researchers from NYU Tandon School of Engineering and Italy's Istituto Superiore di Sanità found that attention-deficit/hyperactivity disorder (ADHD) contributes to obesity not only directly through known biological pathways but also indirectly, by reducing physical activity. The findings are published in PLOS Complex Systems.
Obesity prevalence is also influenced by other city-level variables, such as access to mental health services and food insecurity, thereby opening the door to potential mitigation strategies.
To uncover the nexus between ADHD and obesity, the research team applied urban scaling laws — a mathematical framework from complexity science — to public health data from 915 U.S. cities. Urban scaling describes how features of cities change with population size, similar to how biological traits scale with body size.
They found that both ADHD and obesity decrease sublinearly with population: as cities grow, per-capita prevalence declines. Meanwhile, access to mental health providers and college education rises superlinearly, increasing faster than city size. Larger cities, it seems, offer not just more services, but disproportionately more support for conditions linked to impulsivity.
But size alone doesn’t tell the full story. To reveal where cities over- or underperform relative to expectations, the researchers used Scale-Adjusted Metropolitan Indicators (SAMIs). SAMIs measure how much a city deviates from what urban scaling would predict — highlighting, for example, when a small city has unusually low obesity rates or when a large one falls short on mental health access. These deviations became the foundation for a causal analysis.
"Urban scaling and causal discovery methods allow us to see relationships that traditional health research might miss," explains Maurizio Porfiri, senior author on the PLOS paper. Porfiri is an NYU Tandon Institute Professor with appointments in the Departments of Mechanical and Aerospace Engineering, Biomedical Engineering, Civil and Urban Engineering, and Technology Management and Innovation. He also serves as Director of the NYU Center for Urban Science + Progress (CUSP).
"Without accounting for how city size naturally affects health metrics, we’d misattribute success or failure to the wrong factors. By filtering out these population effects first, we can identify the true causal pathways linking ADHD to obesity — and more importantly, how urban environments modify these relationships,” adds Tian Gan, Ph.D. student in Mechanical Engineering at NYU Tandon. Simone Macrì, senior scientist at the Istituto Superiore di Sanità in Rome, further comments that “This approach reveals precise intervention points that wouldn’t be apparent otherwise"
Using SAMIs, the team mapped a network of interrelated variables: ADHD prevalence led to higher physical inactivity, which in turn increased obesity. Access to mental health care helped reduce inactivity, indirectly lowering obesity risk. Higher prevalence of college education correlated with better mental health access and more physical activity.
This causal map revealed a dynamic system in which impulsivity, health behaviors, and urban infrastructure interact — and cities themselves either reinforce or weaken these effects.
These patterns weren’t uniform. When the researchers mapped SAMIs by region, cities in the Southeastern and Southwestern U.S. consistently showed greater disparities. Neighboring cities often displayed striking differences in ADHD and obesity prevalence, mental health access, and food insecurity — suggesting that local policy, culture, and resources may either amplify or buffer these behavioral health risks.
“Regional averages can mask a lot of variation,” Porfiri said. “The SAMIs let us see which cities are punching above or below their weight. It’s not just about how big a city is — it’s about how it uses its resources. With this kind of insight, policymakers can target investments in mental health care, education, and physical activity to break the link between ADHD and obesity where it's strongest.”
To validate the findings at a more granular level, the team analyzed data from over 19,000 children across the U.S. from the National Survey of Children’s Health. The same causal patterns held: children with more severe ADHD were more likely to be obese, especially when physical activity and household education were low.
The study follows earlier work by Porfiri and collaborators using urban scaling to explore firearm ownership and gun violence across U.S. cities. That research revealed that New York City, despite its large size, significantly outperforms expectations on public safety—underscoring how city-level deviations can challenge assumptions about scale and risk.
In addition to Porfiri, Gan, and Macrì, Rayan Succar, a doctoral candidate in Mechanical Engineering working under Porfiri’s advisement, is also an author on the paper.
The research was supported by funding from the U.S. National Science Foundation and the European Union’s Horizon 2020 programme.
Gan T, Succar R, Macrì S, Porfiri M (2025) Investigating the link between impulsivity and obesity through urban scaling laws. PLOS Complex Syst 2(5): e0000046. https://doi.org/10.1371/journal.pcsy.0000046
