Table 6.

Summary of hierarchical linear regression analyses with socio-demographic, school variables, pupil, parent/guardian e-cigarette use, knowledge, direct and indirect TPB variables as predictors of intentions to use e-cigarettes in young people aged 11–16 years

Step	Predictor variables	R2	∆R2	F, df and p
1	Socio-demographic variables – sex, school year and type	0.076	0.076	F(8, 1386) = 14.22, < 0.001
2	Mothers/female guardian and fathers male guardian EC use	0.097	0.021	F(2, 1384) = 16.41, < 0.001
3	Current pupil EC use	0.295	0.197	F(1, 1383) = 386.7, < 0.001
4	Knowledge of EC	0.296	0.001	F(1, 1382) = 2.76, 0.097
5	Direct TPB measures	0.571	0.275	F(4, 1378) = 220.7, < 0.001
6	Indirect TPB measures	0.653	0.083	F(3, 1375) = 109.2, < 0.001

Step one: socio-demographic and school variables (sex, school year and type). Step two included the addition of mother/female guardian and fathers/male guardian e-cigarette use. Step three included pupil current e-cigarette use, step four saw the addition of knowledge about e-cigarettes. Step five included the addition of the direct measures of attitude, subjective norm, self-efficacy and PBC. Step sex the indirect measures of attitude, subjective norm, and control were added After step one, each subsequent step included the variable(s) from the previous step. Significant (p < 0.05) increases in R² indicated in bold