Operational definitions of four phases of the tobacco epidemic (and number of countries), by sex
| Stages | Female | Male |
| Incipient stage* | Current prevalence <5% (80)† | Current prevalence <15% (17) |
| Phase two | Current prevalence now 5%–45% and never declined, or only declined by <5% points (64) | Current prevalence 15%–65% and never declined or declined by <10% points (85) |
| Phase three | Prevalence has declined by >5% points but is still >20% (27) | Prevalence has declined by >10% points, but is still >25% (52) |
| Phase four | Prevalence has declined by >5% points and is now <20% (33) | Prevalence has declined by >10% points, and is now <25% (50) |
*Countries at this stage, by definition, have never experienced prevalence levels that would classify them to any subsequent epidemic stage; some countries in stage 4 might have similarly low prevalence levels following extensive declines.
†Numbers in parentheses are the number of countries classified into each phase.