As noted in previous GHS reports, it is likely that the GHS underestimates cigarette consumption, and perhaps, though to a lesser extent, prevalence (that is, the proportion of people who smoke). The evidence suggests that when respondents are asked how many cigarettes a day they smoke, there is a tendency to round down to the nearest multiple of ten. Therefore, underestimates of consumption are likely to occur in all age groups.

In relation to prevalence, under-reporting is most likely to occur among young people. To protect their privacy, particularly when they are being interviewed in their parents’ home, young people aged 16 and 17 complete the smoking and drinking sections of the questionnaire themselves, without the questions or their responses being heard by anyone else who may be present, but this is probably only partially successful in encouraging honest answers.

When considering trends in smoking, it is usually assumed that any under-reporting remains constant over time. However, since the prevalence of smoking has fallen, this assumption may not be entirely justified: as smoking has become less acceptable as a social habit, some people may be less inclined to admit how much they smoke, or to admit to smoking at all.