  ######   \(b\) Stratified by income group                           Final adjusted *R*-square value   Model     Standardized coefficients   Sig.   ---------------------- --------------------------------- --------- --------------------------- ---------   Low                    0.000                             Vent      −0.000                      0.000   Per-cigarette weight   0.000                             0.000                                    Filter weight          −0.000                            0.000                                                                                                                                      Middle                 0.000                             Vent      −0.000                      \<0.000   Per-cigarette weight   0.000                             0.000                                    Tipping                −0.000                            \<0.000                                  Filter length          0.000                             \<0.000                                                                                                                                    High                   0.000                             Vent      −0.000                      \<0.000   Per-cigarette weight   0.000                             0.000                                    Tobacco length         −0.000                            0.000                                   [^0]: Academic Editor: 