A new unpublished study has reported finding a 36% increase in heart attacks in Isle of Man following the implementation of an island-wide ban on smoking in public places and workplaces which was implemented in March 2008.
The study compared the number of heart attack admissions in Isle of Man during the two-year period prior to the smoking ban with the number of heart attack admissions during the two-year period following the smoking ban.
Because Isle of Man is an island with only one hospital, it serves as an excellent location in which to study changes in heart attack admissions in association with a smoking ban.
The study findings are presented as follows: "Before the smoke free legislation was introduced, myocardial infarctions episodes (admissions) were increasing at a rate of 0.23 per month. This means that roughly every 4 months there would be, on average, one more patient admitted with myocardial infarction in the Isle of Man than the previous 4 months? In the 2 years after the legislation was put in place, the results show that there was no longer an average increase."
The study conclusion is as follows: "This study provides some evidence which, together with related studies carried out in different countries, demonstrates that laws enforcing smoke free regulations in public areas may be associated with a reduction in myocardial infarction admissions and so a concomitant reduction in the incidence of MI in the population."
A press release accompanying the study report asserted that: "The statistical analysis of the data shows that there was a significant reduction in the rate of admissions to Noble’s Hospital for heart attacks amongst males aged over 54." The press release concluded that: "We are pleased to be able to demonstrate a local positive health effect resulting from the tobacco legislation."
The press release was picked up by several news outlets. For example, a headline on the BBC News web site boasted: "Isle of Man smoking ban 'cuts heart attacks'."
The Rest of the Story
You are probably wondering - how could the study and press release conclude that the Isle of Man smoking ban cut heart attacks if the number of heart attack admissions increased by 36%?
The answer is simple: sleight of hand.
When the researchers found that heart attacks went up, not down, in Isle of Man after the smoking ban, they apparently used a trick to make it appear that the smoking ban decreased the number of heart attacks. What they did was to examine the difference in the rate of change in heart attacks from before to after the smoking ban.
This technique is fine when you have many years of data, so that you can accurately determine the rates of change in heart attacks. However, with just two years of data in the baseline period, it is not possible to accurately determine the rate of change in heart attacks.
The fact remains that the major finding of the study is that there was an increase, not a decrease in the number of heart attack admissions following the smoking ban. Here are the actual results:
During the period April 2006 through February 2008 (prior to the smoking ban), there were 216 heart attacks, or a rate of 9.4 heart attacks per month.
During the comparable period April 2008 through February 2010 (after the smoking ban), there were 293 heart attacks, or a rate of 12.7 heart attacks per month.
Thus, the heart attack rate increased from 9.4 heart attacks per month to 12.7 heart attacks per month, an increase of 36%.
If one compares the number of heart attacks during comparable months from before to after the smoking ban, it turns out that for 20 of the 23 months, heart attacks went up. For 2 of the 23 months, heart attacks went down. For 1 of the 23 months, heart attacks were the same.
To interpret these data as showing evidence of a significant decline in heart attacks associated with the smoking ban is beyond comprehension.
This study is truly an example of playing with statistics in order to try to support a pre-determined conclusion, rather than simply reporting objectively the findings of an analysis.
Unfortunately, the improperly interpreted and grossly distorted results of this study have been disseminated widely throughout the world via the media. Headlines such as: "Heart Attack Rates Fall Following Smoking Ban" are spreading rapidly. What the public is not being told, however, is that this study actually found a 36% increase in the number of heart attack admissions in the two years following the smoking ban.
To make it clear, I am not arguing here that the smoking ban caused an increase in heart attacks. The number of heart attacks is extremely small and there are many other factors related to changes in heart attack rates. However, what is clear from this study is that it absolutely does not provide evidence that the smoking ban resulted in a decrease in heart attack admissions in Isle of Man. Any group which is disseminating such a conclusion is spreading scientifically shoddy information.
For more on this story, don't miss Christopher Snowdon's post over at Velvet Glove, Iron Fist, where he dissects this study in a way very similar to my own analysis.