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Table 4 Average increase in cotinine concentration (ng/ml) in adult daily smokers per one cigarette smoked in the previous 24 hours by type of regression model.

From: Salivary cotinine concentrations in daily smokers in Barcelona, Spain: a cross-sectional study

Estimation of model β * 95% CI R 2 p-value
Men (n = 103)     
simple linear model 5.3 3.5, 7.2 0.244 ----
quadratic model 15.7 9.0, 22.3 0.313 < 0.05
quadratic model adjusted for covariates 14.8 8.1, 21.5 0.353 < 0.05
Women (n = 104)     
simple linear model 7.7 5.9, 9.5 0.412 ----
quadratic model 11.2 5.7, 16.7 0.421 0.188
quadratic model adjusted for covariates 11.3 5.8, 16.7 0.458 0.078
  1. Barcelona (Spain), 2004-2005.
  2. β for the simple variable "number of cigarettes smoked in previous 24 hours" (for one cigarette smoked)
  3. p-value for the change of fit between the adjusted models and the simple linear model adjusted for age, educational level, and body mass index