Previously published meta-analyses of smoking behavior have used 2 different codings of CPD: (1) heavy smoking (CPD >20) vs light smoking (CPD ≤10), excluding the intermediate group,19 and (2) CPD as a linear variable coded 0 (CPD ≤10), 1 (CPD of 11–20), 2 (CPD of 21–30), and 3 (CPD >30).16–18 We used both variables for these meta-analyses. The 2 variables gave similar beta values and statistically similar results. For ease of interpretation, results are reported for heavy vs light smoking. The results using CPD as a linear variable are given in eTable 2.
