  ######   \(b\) Stratified by income group                           Final adjusted *R*-square value   Model     Standardized coefficients   Sig.   ---------------------- --------------------------------- --------- --------------------------- ---------   Low                    0.000                             Vent      −0.000                      0.000   Tobacco length         −0.000                            0.000                                                                                                                                      Middle                 0.000                             Vent      