TABLE 3.

Adjustment for smoking: ratings and frequencies

Type of smoking adjustment and effectiveness score	Number of samples (n = 36)	Assessment
Level 1. Binary variable Current smokers vs. nonsmokers	9	Least effective type of adjustment with former smokers included with never smokers
Level 2. Smoking status Use of 3 categories: current, former, never smokers	7	Commonly coded as 2 binary variables. Ineffective adjustment where there are nonlinear associations between smoking and coffee consumption
Level 3. Smoking status and intensity One or more smoking variables with ≤4 categories based on smoking status and intensity	7	More effective adjustment than smoking status but limited number of intensity categories does not effectively adjust for nonlinear associations
Level 4. Complex adjustment Multiple smoking variables including smoking status, intensity and cessation time, or pack-years of smoking	13	Most effective type of statistical adjustment, using pack-years of smoking, time since cessation, or similar measures