Subsample/polydrug use pairing
      Alcohol/tobacco users Alcohol/cannabis users Tobacco/cannabis users
Frequent SPU Cross-SPU One substance triggers the other and vice versa
Partial SPU Alcohol cue Alcohol triggers tobacco use Alcohol triggers cannabis use  
Smoking cue Smoking triggers alcohol use   Smoking triggers cannabis use
Cannabis cue   Cannabis triggers alcohol use Cannabis triggers tobacco use
Non/rare SPU Substances are rarely or never used at the same time
Table 1: The different kinds of simultaneous polydrug use measured