Understanding Sex Differences in Disease Trajectories

A geometry-informed approach to measuring how 10 major chronic conditions evolve as populations age across the US, Western Europe, and Japan.

1 Mapping Aging on a Curved Surface

Instead of plotting these factors on a flat graph, the study models them as dynamical systems embedded in a curved geometric space called the hyperbolic plane. As a population ages, they move across this map, tracing a distinct trajectory. This non-Euclidean geometry is uniquely suited for statistical distributions.

Graph showing the trajectory of chronic respiratory diseases in the male population over time
Male Trajectory
Graph showing the trajectory of chronic respiratory diseases in the female population over time
Female Trajectory
Visualizing the "path" of chronic respiratory diseases in California (1990). The markers indicate successive 5-year age groups.

2 Why the Fisher-Rao Distance?

To measure the total "length" of these epidemiological shifts, the study utilizes the Fisher-Rao distance. When tested against alternatives like Kullback-Leibler (KL) divergence, absolute mean differences, and absolute standard deviation differences, the Fisher-Rao metric demonstrated significantly greater cross-regional consistency.

Line graph displaying cumulative Fisher-Rao distance across different age cohorts
Cumulative Fisher-Rao distance measuring the total shift across age cohorts. A steeper line represents a more significant epidemiological change over time.

3 Findings Across 10 Chronic Conditions

By comparing the total trajectory lengths between males and females from 1990 to 2019, distinct patterns emerged:

Greater Shifts in Males

Longer trajectory shifts were consistently observed in:

  • Neoplasms (Cancers)
  • Cardiovascular diseases
  • Chronic respiratory diseases
  • Diabetes and kidney diseases
  • Skin and subcutaneous diseases
  • Sense organ diseases

Greater Shifts in Females

Longer trajectory shifts were consistently observed in:

  • Neurological disorders
  • Mental disorders
  • Substance use disorders

Mixed / Variable Patterns

Digestive diseases lacked a uniform sex-based shift globally. They showed no significant sex differences in the United States or Western Europe, but exhibited a male predominance in Japan.

Explore the Methodology

The full data cleaning pipelines and statistical analyses are open-source.

View GitHub Repository