- (2) _hi(t) = ho1(t) exp (xi’β)_ if individual _i_ is in group 1 _hi(t) = ho2(t) exp (xi’β)_ if individual _i_ is in group 2.

Table 2 presents results where the data have been stratified by gender, race, and year of birth as well as by age at interview and by the year of the interview, since the data is constructed from smoking histories taken from interviews ranging from 1978 to 2000. Table 2 indicates that, among smokers, the probability of smoking cessation at any point in time increases highly with education. The very significant results indicates that, for all decades and all birth cohorts, an additional year of education increases by 7.6 percent the probability that that person will quit smoking.<sup>17</sup> Table 2 further analyzes the effect of education on the incidence of smoking cessation by dividing the sample across birth cohorts and across decades. The first row shows the effect of education on the probability of smoking cessation during the 19402000 period, by 10-year birth cohort, from the cohort born between 1910 and 1920 and the cohort born between 1970 and1980.<sup>18</sup> The effect of education appears to be increasing from earlier to later birth cohorts, with some leveling off for the three last birth cohorts. However, across birth cohorts the period considered as well as the age ranges considered varies widely. One constant, if we exclude the 1940-1950 decade, is that, reading each row horizontally from right to left, during each decade, the younger the individuals, the stronger the effect of education on smoking cessation.

The first column of table 2 shows the effect of education on the probability of smoking cessation for all birth cohorts, decade by decade, during the 1940-2000 period. The effect of education increases steeply from the 1940s to the 1950s and further from the 1950s to the 1960s, while the information on the dangers of smoking start to diffuse. The effect of education is still strong, but reaches a plateau thereafter. Again, however, the composition of the sample for each decade varies widely in terms of birth cohort and age ranges. In this respect, an analysis following each cohort separately from decade to decade is more interesting.

When table 2 is read vertically by birth cohort the striking result is for the four birth cohorts of smoking age during the 1950-1970 period. When the information on the health

> 17 When looking at education categories, compared to individuals with less than a high school education, high school graduates are 23.1 percent are more likely to quit smoking; individuals with some college education are 46.8 percent more likely to quit smoking; and college graduates 106.1 percent more likely to stop smoking. These results also hold when the sample is divided across genders: the point estimates are slightly higher for females, but qualitatively they are similar.

> 18 Notice that for this birth cohort, since I only consider individuals above age 25 and since the last survey used is from 2000, the survival analysis actually follows individuals born between 1970 and 1975 interviewed during the 1995-2000 surveys, while they were between ages 25 and 30. _Mutatis mutandis_ , the same reasoning applies to the last cell of each row.

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