1. University of Michigan School of Public Health
Smoking disparities by education attainment in the United States,
Pianpian Cao
University of Michigan School of Public Health
WCTOH, March 9, 2018
Cape Town, South Africa
Good afternoon everyone, thank you for being my audience today on a wonderful Friday afternoon in Cape Town. I’ll be talking about smoking disparities by education in the United States. You will be able to learn more about smoking patterns by education at a finer level and hopefully the study results can be useful to inform targeted health programs and campaigns.

2. Background
Previous studies found higher smoking rates among those with lower education
Less is known about
Smoking patterns by birth cohort
Difference in smoking behaviors between those with less than 8th grade education and those with 9-11 years of education
How the relationship between smoking and education varies by race, birth place and birth cohort
So a brief background before I dive into interesting methods and results. Previous studies have identified higher smoking rates among those with lower education. However, less is know about smoking patterns by birth cohort, whether there exists any difference in smoking behaviors between those with less than 8th grade and those with 9-11th grade education as those two groups are usually combined into one. Finally, we also know little about how the relationship between smoking and education varies by race, nativity and birth cohort. Therefore, our study was conducted to address these gaps.

3. Approach-1 Data: National Health Interview Series, 1966-2015
Age: 25-84
Education categories: 1) ≤8th grade, 2) 9-11th grade, 3) high school graduate or GED, 4) some college, and 5) college graduate or above
Models: age-period-cohort models with constrained natural splines
Outcomes: initiation and cessation probabilities, smoking intensity, and ever-/never/current/former smoker prevalence
The first approach we took is by using the National Health Interview Series, which is a national representative annual health surveys of United States. What is great about this survey is that it is one of the oldest national survey on health in the U.S. starting as early as 1965, and it collects detail information on smoking behaviors, from starting age, year since quit to how many cigarettes smoked per day.
In our study, we are using the NHIS 1966 to 2015 data, with a constraint on age being 25 or above as education is usually settled after that age. We classified education into 5 categories, being …(General equivalency diploma)… We applied an age-period-cohort model with constrained natural splines to study the patterns. And our outcome, benefit from the abundant data and flexible modeling approach, includes initation and cessation probabilites, smoking intensity and different smoking prevalence by age, birth cohort, gender and education level.

4. Results-1: Initiation probability for males
Now I’m going to talk briefly about results of approach 1. This figure is showing the initiation probabilities for men by birth cohort. The x-axis is age. And the 5 colored lines represent the 5 education groups mentioned earlier. We can see from the figure that the initiation probabilities decreased by birth cohort, which is encouraging. 9-11TH graders have consistently higher initiation rate than the other groups, which is the yellow line. Now I would like to draw your attention to the two dotted lines, black and red. The black dotted line represents college graduate or above while the red line is less than or equal to 8th grade education. The college or above education group has consistently lowest initiation prob, while for the lowest education group, less than or equal to 8th grade education, although it first started high, it dropped dramatically and became the second lowest in the 1980 birth cohort.
The pattern for women which is not shown here is similar except they picked up smoking later.
The figure for smoking cessation probabilites, which is also not shown, shows that cessation probabilities increased by birth cohort and consistent with other studies, the relationship between cessation and education is linear, meaning higher education is more likely to quit.

5. Results-1: Current smoker prevalence for males
Initiation and cessation probabilities together can inform us about current smoker prevalence. Same story: current smoker prevalence among those with less than or equal to 8th grade started out to be highest in the 1920 birth cohort, which later on drop dramatically across birth cohort, and became the second lowest.
This pattern was not presented in any of the previous studies, and thus we decided to conduct a second set of analyses trying to understand why.

6. Approach-2 Data: National Health Interview Series, 1997-2015
Smoking Status
Age, Year, Sex
Race/Ethnicity,
Nativity
Education
Figure 1. Conceptual framework
Data: National Health Interview Series,
Age: 25-84
Exposure: education attainment (5 categories)
Outcome: ever-smoked (binary)
Explanatory analysis and logistic regression
In the second approach, we decided to take a more epidemiological route. Figure 1 shows the conceptual framework of the analysis. The confounders, which is the variables that masks the true relationship between education and smoking, are age, year…. We used the NHIS 1997 – 2015 data as one of our important confounders, nativity, was collected since 1997.
The same age constraint and classification for education. Currently, we only considered ever smoking prevalence, defined by whether someone smoked more than 100 cigs in their life time, but will expand our analyses further to characterize current smoking prevalence.

7. Results-2: Distributions of race/ethnicity are different across education groups
According to our explanatory analysis, the distribution of race/ethnicity are very different across education groups. We have five categories for race/ethnicity: american indian/alaska native, asian pacific islander, hispanics, non-hispanic blacks and non-hispanic whites. On the left panel of the figure, it is showing the proportion of each ethnicity groups in the <=8th grade education group, across year. We can see that HISP dominates the lowest education group in recent years, while completely different story for college graduate or above showing in the right panel. NHW dominates this group over years.

8. Results-2: Ever-smoker prevalence is lower among non-US born individuals, and Hispanics and API ethnicity groups
We also explore the relationship between ever smoking and the covariates. These two plots show that ever-smoker prevalence is lower among non-US born individuals and Hispanics and API ethnicity groups

9. Results-2: Nativity is a strong effect modifier of the relationship between education and smoking
ODD RATIO*
All
US-born
Non-US born
<=8th grade vs. College
2.77 (2.65, 2.90)
4.27 (3.99, 4.58)
1.29 (1.19, 1.39)
9-11th grade vs. College
4.80 (4.63, 4.97)
6.22 (5.96, 6.49)
1.54 (1.41, 1.67)
High school or GED vs. College
2.77 (2.70, 2.84)
2.98 (2.90, 3.06)
1.56 (1.47, 1.66)
Some college vs. College
2.23 (2.18, 2.28)
2.32 (2.26, 2.38)
1.72 (1.61, 1.84)
Finally, we conducted several logistic regressions to understand the effect of education on smoking adjusting for confounders. This table shows the odds ratio of ever smoking comparing highest education group and the other four groups.
You can see in the first column, after adjusting for all covariates, being …., the odds of ever-smoking among the “<=8th grade” education group is the third lowest, and significantly lower than the odds among those with 9-11th grade.
On the other hand, if we restricted the analysis to US-born only, the odds of ever-smoking among those with <= 8th grade now become the second highest; on the contrary, when looking at Non-US born only, the odds of ever-smoking in the lowest education group now become the second lowest.
Therefore, nativity is a strong effect modifier and confounder of the relationship between education and smoking. This also makes us speculate that Recent low smoking rates among the ”<= 8th grade” group is partly driven by the influx of Hispanic immigrants in the 80s and 90s
* Adjusted for sex, age, race/ethnicity, year and (nativity for non-stratified analysis)

10. Conclusions
Our study provides detailed insights into smoking patterns across 5 education groups by birth cohort
Initiation probability and smoking prevalence among the ”<= 8th grade” education group are the second lowest for recent birth cohorts
Identified population characteristics that drive the changes in smoking patterns by education
Recent low smoking rates among the ”<= 8th grade” group is partly driven by the influx of Hispanic immigrants in the 80s and 90s
In conclusion, our study found a low smoking rates among the lowest education group and such low smoking rates may be driven by the influx of Hispanic immigrants since 1980s.

11. Acknowledgments
Co-authors: Theodore R. Holford, Jihyoun Jeon, Jamie Tam, Nancy L. Fleischer, Rafael Meza 
David Levy and the rest of the Cancer Intervention and Surveillance Modeling NETwork (CISNET) lung group
Funding – CISNET grant NCI U01CA199284
Thank you for your attention!