(b) Stratified by income group

	Final adjusted R-square value	Model	Standardized coefficients	Sig.
Low	0.561	Vent	−0.037	0.909
		Tobacco length	−0.857	0.047
Middle	0.894	Vent	0.055	0.795
		Tipping	−2.139	<0.001
		Filter length	2.212	<0.001
		Number of rows	−0.547	0.014
		Per-cigarette weight	0.620	0.015
		Cigarette length	−0.391	0.072
High	0.956	Vent	−0.897	<0.001
		Tipping	−0.308	0.015
		Number of rows	0.266	0.009
		Per-cigarette weight	0.522	<0.001
		Cigarette length	−0.204	0.055
		Filter diameter	0.282	0.004