Pack size, reported cigarette smoking rates, and the heaviness of smoking.

Three distinct samples show that pack size is highly associated with individual reports of daily cigarette intake, confirming an earlier report based on aggregate data. Those who report smoking 25 cigarettes per day (or who buy packs of 25) are heavier smokers than those who report smoking 20 cigarettes per day (or who buy packs of 20), as evidenced by greater likelihood of starting smoking earlier in the morning and by higher average levels of alveolar carbon monoxide. Categorizations based on number of cigarettes smoked per day should not assume that "one pack of twenties" is roughly the same as "one pack of twenty-fives." No conclusions can be drawn about whether the availability of larger packs promotes heavier smoking.