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Table 4 Non-chemical triggers and COPD exacerbation (Weather, flu, and physical activity)

From: Low level air pollution and exacerbation of existing copd: a case crossover analysis

Variable type Variable description Odds ratio 95 % confidence interval −2loglikelihood
Weather Spent time in cold air/cold weather in past weeka 1.16 0.78 1.70 468
Spent time in hot air/hot weather in past weeka 0.50 0.34 0.75 457
Local Temperature (linear 7 day average)b 0.96 0.95 0.98 445
Local Temperature (categorical)c
 Cool/Cold 1.0 1.0 1.0 422
 Moderate 2.50 1.51 4.12
 Warm/Hot 0.55 0.36 0.84
Local Relative Humidity (linear 7 day average)b 0.98 0.96 1.01 471
Local Relative Humidity (categorical)c
 High 1.0 1.0 1.0 471
 Low 1.21 0.84 1.73
Season Season, ref = summer
 Summer 1.0 1.0 1.0 417
 Spring 2.59 1.55 4.35  
 Winter 2.38 1.37 4.11  
 Fall 6.64 3.83 11.5  
Acute Illness Respiratory infection/cold in past weeka 8.14 4.67 14.2 396
Non-respiratory Illness in past weeka 1.65 0.67 4.05 422
Sinus infection in past weeka 2.55 1.20 5.44 461
Regional Flu Trends; New Englandd 3.78 1.54 9.28 463
Physical Activity Total hours spent outside of the homea, e 0.99 0.99 1.00 469
Exercised in past weeka 0.60 0.39 0.93 462
  1. aBased on self-reports from exposure questionnaires
  2. bBased on 7-day averages using data from NOAA collected at Worcester Regional Airport
  3. cCategorical representation of variable based on cut-offs identified in restricted cubic splines
  4. dRegional proxy of flu from CDC data; represented by percent of weekly outpatient visits for influenza-like-illness in New England
  5. eEstimated as sum of “Hours Reported Outdoors”, “Hours Reported in a Vehicle”, and “Hours Reported Indoors but not at home”