New data published by Christopher Snowdon over at his blog Velvet Glove Iron Fist reveal that the conclusion by Pell et al. (published in the New England Journal of Medicine in July 2008) that hospital admissions for acute coronary syndrome in Scotland fell by 17% after implementation of the national smoking ban is incorrect.
The data presented by Pell et al. were incomplete in four major ways. First, they only reported data for the 10-month period preceding the smoking ban and the same 10-month period following the ban. The two months immediately following the ban were ignored, as were the same two months in the previous year. Second, Pell et al. only presented data for 10 months, which does not allow enough time to determine whether the observed trends were real (sustained) or just statistical artifacts. Third, Pell et al. did not go back in time to examine the baseline trends in acute coronary syndrome admissions. Finally, the study only examined data for a sample of hospitals in Scotland, not for the entire country.
In the present study, Snowdon obtains a complete data set of acute coronary syndrome admissions in all of Scotland for the entire period from 1999 through 2007. He includes data for the full two years following the smoking ban and for at least seven years preceding the ban.
Snowdon finds that contrary to the results reported by Pell et al., acute coronary syndrome admissions fell by just 9.3% in the year following the ban (compared to the year preceding the ban). But more importantly, this decline is no greater than that observed several times during the baseline period. For example: "AMI [acute myocardial infarction] admissions fell by 10.2% in 1999-2000 and angina admissions fell by 10.5% in 2005-2006 (there were also falls of 11.6%, 11% and 12% in previous years)."
Moreover, when one examines the full data, one sees that while there was a decline in acute coronary syndrome admissions in Scotland following the smoking ban, this decline was not as steep as it had been prior to the smoking ban. In other words, the rate of decline in acute coronary syndrome admissions actually decreased after the smoking ban.
The Rest of the Story
The data from 2007 make it clear that the Pell et al. conclusion is invalid. In that study, they looked at such a small snapshot in the data that they missed the overall pattern, which clearly shows that instead of there being a striking decline in acute coronary syndrome admissions, there has actually been a leveling off of the steep trend of declining admissions.
This analysis demonstrates why one has to be extremely careful in drawing causal conclusions when using time trend data and only examining brief snapshots in time. Time series studies must be conducted using all available data for long periods before and after the event of interest.
What is most interesting to me, however, is not that the conclusions of the Pell et al. study are invalid and that the trend they reported turns out not to be accurate. What is most interesting to me is the apparent bias in the research on this topic of smoking bans and heart attacks. It very much appears that researchers want to find an effect of smoking bans on heart attacks (which is understandable) and that they are subconsciously analyzing the data in such a way as to find such a pre-determined conclusion.
Look - you're hearing this from someone who has staked his career on the need for smoking bans, who has testified in support of smoking bans in more than 100 cities and states, who has published research on the health benefits of smoking bans, and who would therefore love nothing more than to find out that his work is helping to reduce heart attacks over a short term period. If anything, I should be strongly biased in favor of interpreting these data such as to find an effect.
However, these data are just so unconvincing that even I cannot, with any conscience, look at them and opine that they show a significant short-term effect of smoking bans on heart attack admissions (or acute coronary syndrome admissions). If anything, these data suggest that there was not any significant effect of the smoking ban on acute coronary syndrome admissions.
The unconscious bias in anti-smoking research is understandable to me, because I have come to realize that there is an extreme pressure in the movement to publish research that is favorable to the cause. The rewards go not to the scientists in the movement who are objective and committed to seeking out and reporting the truth. The accolades and acclaim go to those who report favorable results.
In other words, the value of scientific accuracy and scientific integrity is no longer recognized in the movement. It is now all about the direction of the findings.