Thursday, January 12, 2017

CDC Omitted Important Findings in Report on 2015 National Youth Tobacco Survey

The U.S. Centers for Disease Control and Prevention released selected information from the 2015 National Youth Tobacco Survey in April 2016 (here).  The agency cherry-picked numbers from previous surveys to portray e-cigarettes as a threat to teens, while ignoring sharp declines in teen smoking (here, here and here).

Last month, the CDC released the underlying 2015 NYTS data, ending an eight-month embargo that prevented analysis by independent investigators. 

The agency traditionally reports current smoking and vaping numbers separately, ignoring dual use and wrongly suggesting that the numbers are independent.  In contrast, here I report exclusive users of these products as well as dual users.  I also add important findings that the CDC omitted.

The chart shows current use (that is, on one or more days in the past 30) of cigarettes and e-cigarettes among middle and high school students over the four-year period.  The CDC emphasized the large increase in e-cig use from 2011 to 2015.  As I noted earlier (here), the large spike from 2013 to 2014 was likely due to a change in the NYTS questions.  It is clear that the increase slowed during the last year, but prevalence of exclusive e-cig use among high schoolers still  increased from 8.2 to 10.6%; dual use declined marginally from 5.2 to 5.0%.  The prevalence of exclusive smoking among high school students was flat at 4.0%. 

Given that the CDC has relentlessly asserted that e-cigarettes are a gateway to smoking, it is unsurprising that the agency did not publicize responses to two questions in the 2015 survey that focused on which products students used first.  I report here for the first time how high school students answered these questions, comparing two groups of current smokers: those who only smoked cigarettes and dual users of cigarettes and e-cigs.

The question, “Which of the following tobacco products did you try first?” produced these results:

Table 1. Percentage of High School Current Exclusive Smokers and Dual Users Who Tried Various Tobacco Products First, NYTS 2015
ProductExclusive SmokersDual Users

Smokeless tobacco9.17.6
Other products1.12.6
Not sure2.91.3
Never tried any product4.40.3

Percentages in bold: Exclusive smokers significantly different than dual users.

The table shows that there were no significant differences between exclusive smokers and dual users in the product first used.  Most had tried cigarettes first (60% and 67% respectively); the rest had chosen cigars, smokeless, e-cigs and other products.  There is little evidence here for the CDC’s claim that e-cigarettes are a gateway to smoking.

A question about initiation further exposed the relationship between cigarette and e-cigarette use.  Here is how current exclusive smokers and current dual users responded:

Table 2. Relationship of Cigarette and E-Cigarette Use Among High School Current Exclusive Smokers and Dual Users, NYTS 2015
ResponseExclusive SmokersDual Users

Never tried cigs or e-cigs16.4%1.8%
Only tried cigs19.82.7
Only tried e-cigs0.51.9
Tried cigs before ever tried e-cigs48.777.2
Tried e-cigs before ever tried cigs 14.616.4

Percentages in bold: Exclusive smokers significantly different than dual users.

This table shows that large majorities of high school current exclusive smokers and dual users started with cigarettes.  Only 15-16% of these students are even eligible to be considered gateway cases, in which users moved from vaping to smoking.

There are troubling inconsistencies in these tables.  For example, 16% of current exclusive smokers – who only used cigarettes in the past 30 days – responded that they never tried cigarettes (Table 2).  Four percent of exclusive smokers responded that they had never used any tobacco product (Table 1).

The “Y” in NYTS stands for youth, and responses from these surveys are known to be inconsistent.  In working with the data, if one eliminates participants who gave inconsistent responses, there would be considerably fewer valid participants.  I discussed this problem in 2015 (here), when I called on the CDC to “issue a comprehensive report on the internal consistency and relative validity of the NYTS data.” The agency appears to have ignored that issue.

1 comment:

Lollylulubes said...

They should also have asked how many actually use nicotine in their ecigs.