Table 1

Summary characteristics of participants by country

AustraliaCanadaUKUSATotal
N5794785123671936
Age in years at baseline*** (SD)42.9 (13.2)a 44.6 (13.9)a 49.4 (13.3)b 49.7 (15.7)b 46.3 (14.2)
Sex (%)
 Male48.943.342.440.944.3
 Female51.156.757.659.155.7
Socioeconomic status (%)***
 Low17.313.828.715.519.1
 Medium56.653.649.850.452.9
 High26.232.621.534.128.0
HSI while smoking (%)***
 030.822.719.519.023.6
 115.915.111.316.814.6
 217.017.623.419.919.4
 319.822.524.926.323.0
 411.214.216.710.413.3
 53.77.02.55.14.5
 61.70.91.72.51.6
Baseline quit length in days (SD)127.7 (107.1)128.0 (107.7)132.4 (103.2)126.1 (106.8)128.7 (106.1)
Per cent relapsed at follow-up (%)43.443.740.742.242.5
  • HSI, 0 = lightest to 6 = heaviest. This is the categorical version of HSI, measured approximately 1 year prior to quit baseline while participants were still smoking—for the regression analyses, the continuous version was used, calculated by subtracting the natural logarithm of minutes to first cigarette from the square root of cigarettes per day. Data on HSI were missing for 8.4% of participants. Post-hoc comparisons (Bonferroni corrected, α=0.0084) revealed significant differences in age between countries with different superscripts.

  • ***p<0.001 (global analyses of variance and χ2 comparisons).

  • HSI, heaviness of smoking index.