text: (eg, climate, air quality/industrialization, socioeconomic 
  status) of the catchment population tend to vary across 
  study sites. 
  
  Approximately 65% of the variability in dyspnea 
  remained unexplained by the factors examined in our 
  study. Most individuals in our study showed normal 
  spirometry results but still carried a substantial 
  burden of dyspnea, an inconsistency that needs 
  explanation. Several factors not included in our 
  analysis may have contributed to the unexplained 
  variation. Environmental factors (eg, air pollution, 
  allergen exposure, seasonal variations in symptoms) 
  are potential contributors to this unexplained 
  variability.22 Genetic predispositions could also play a 
  signiﬁcant role, as suggested by a study that revealed 
  that parents with dyspnea were 1.8 times more likely 
  to have offspring with dyspnea.23 Additionally, ﬁtness 
  could be a contributing factor, especially in 
  individuals with undiagnosed PRISm, asthma, or 
  COPD who may restrict their activities to avoid 
  dyspnea, and hence become deconditioned.6 
  
  Dyspnea is a complex, subjective symptom that is 
  modiﬁed by nonrespiratory factors including 
  psychosocial, social, and environmental inﬂuences.5 
  Interindividual variability in the perception of dyspnea, 
  inﬂuenced by these nonrespiratory factors, may play an 
  important role. A study conducted by Ziegler et al24 
  assessed the perception of dyspnea in 42 healthy 
  individuals using a standardized inspiratory resistive 
  loading stimulus. The study used the modiﬁed Borg 
  scale to measure dyspnea perception levels. Among the 
  participants subjected to the same inspiratory resistive 
  load, 31%, 45%, and 24% of participants classiﬁed their 
  level of dyspnea as low, intermediate, and high, 
  respectively. The study revealed that differences between 
  individuals contribute considerable variability to the 
  perception of dyspnea, even among healthy participants. 