prevalence. The prevalence of smoking among individuals with less than a high school degree is 29.6 percent, 28.4 percent for high school graduates, 25.6 percent for people with some college education, but only 14.2 percent of people with at least a college degree smoke. The most striking feature of figure 2 is that smoking prevalence among the college graduates declined earlier and more dramatically. This declining trend starts in 1954, 10 years before the first Surgeon’s General Report and only one year after the first articles in the general press. Differences in smoking prevalence among the three lower education categories are less marked, but a careful examination of figure 2 reveals, however, that the ranking between these three categories has been inverted between 1940 and 2000. Figure 2 clearly supports the idea that more educated people reacted more quickly and more strongly to the information about the health damaging consequences of smoking.<sup>6</sup> Keep in mind that in this analysis the general level of education in the population has been steadily increasing between 1940 and 2000. Being a college graduate in 1940 was more exceptional than it was in 2000. Figure 3 addresses this question by plotting the smoking prevalence among individuals above or under the average education level in each year for individuals aged 25 in that particular year.<sup>7</sup> Initially, individuals above the average education level were more likely to smoke. The positive difference between the prevalence in both groups has been gradually decreasing and now the situation has been inverted, since individuals under the average schooling level in the population are much more likely to smoke.

# **_2.3 Sample Composition Issues_**

The retrospective smoking histories allow a complete overview of smoking prevalence patterns by education levels from 1940.<sup>8</sup> However, this method presents two problems in the composition of the sample. First, since the information about smoking prevalence between 1940 and 1977 is gathered from surveys taken between 1978 and 2000, only individuals who survived up to the year of the survey are interviewed. Since smokers usually die sooner than nonsmokers, this creates a ‘‘survivor’’ bias: nonsmokers are disproportionately represented among persons interviewed at older ages. This problem is avoided by selecting respondents less than 60 years of age at the time of the survey. Even though there is already some excess mortality due to smoking before age 60, most of

> 6 De Walque (2003) confirms that this general picture is valid when males and females are analyzed separately.

> 7 In 1940, the average education level was between 10 and 11 years of education, in 1954 it went above 11 and in 1976 it went over 12. This explains the discontinuity in 1976, since in that year high school graduates, who were previously above the average, fell under the average.

> 8 I have compared current smoking prevalence rates by education from 1974 to 1999 as calculated directly from the yearly National Health Interview Survey with the estimates obtained in this paper using retrospective smoking histories constructed from 16 surveys. The estimates using these two methods are very close. Results are available on request from the author.

5