Table 1

 R2 values for the introduction of independent variables at each step in stepwise multiple regression models for tar, nicotine and carbon monoxide under ISO conditions

Tar (CtarISO)Nicotine (CnicISO)CO (CcoISO)
C, concentration; ISO, International Organization for Standardization; NISO, number of puffs; S, paper porosity; Vf filter ventilation; W, weight of tobacco filter.
Note that filter ventilation (Vf) is introduced in step 1 as the first (most important) explanatory variable, with very high R2 values for all three emissions. Values of F and associated degrees of freedom (df) as well as the regression coefficients are given for each model.
Step 1 variable Vf Vf Vf
    R20.9030.8530.892
Step 2 variable NISO NISO W
    R20.9330.9400.942
Step 3 variableS
    R20.951
Model intercept8.5600.3467.142
    β1−0.174Vf−0.012Vf−0.133Vf
    β20.799NISO0.095NISO10.128W
    β3−0.022S
    F (df)321.8 (2, 46)358.8 (2, 46)292.9 (3, 45)