We voorspellen het nu alvast: de politici in de Tweede Kamer zullen binnenkort weer een nieuw argument aangevoerd krijgen door de anti-rokenlobby. Een nieuw onderzoek zou aantonen dat na de invoering van het rookverbod in Ierland het aantal hartaanvallen met 15% is gedaald.
Nee, zegt Dr. Michael Siegel, dit is weer eens een voorbeeld van de aanpak zoals we die eerder gezien hebben bij de Helena en Piedmont onderzoeken: er is weer nauwgezet een periode en regio geselecteerd waarin deze stelling aangetoond kan worden. Maar in feite kan het net zo goed een toevallige samenloop van omstandigheden zijn. De onderzoekers hebben daar niet op getest en kunnen niet aantonen, door maar een periode van negen maanden te analyseren, dat de (tijdelijke?) afname van opnames van slachtoffers van hartaanvallen te wijten is aan het rookverbod.
Steeds meer onderzoeken in de anti-rokenwereld formuleren eerst een conclusie en gaan dan op zoek naar de cijfers om die te staven. Hier hebben we daar weer een goed voorbeeld van.
A new study presented this week at the annual scientific symposium of the European Society of Cardiology concludes that the smoking ban in Ireland resulted in a 14.5% decline in heart attack hospital admissions during the first year after its enactment.
A Reuters article from yesterday boasts: “Heart attacks tumble after Irish smoking ban” and quotes the study authors as arguing that their research demonstrates the need for further smoking bans.
According to the article: “Ireland’s rate of heart attacks fell by around a tenth in the year following the introduction of the world’s first nationwide ban on workplace smoking, boosting the case for more similar bans, doctors said on Tuesday. Edmond Cronin and colleagues at Cork University Hospital said an analysis of people admitted with heart attacks to public hospitals in southwest Ireland showed an 11 percent fall in the year after the ban came into effect in March 2004.”
In a Telegraph article, the lead study author was quoted as stating: “A national ban on smoking in public places resulted in a decrease in admissions for heart attack, especially in smokers. Our study provides evidence of the rapid effect of banning smoking in public places on decreasing the burden of heart attacks.”
The Rest of the Story
What these news articles and quotes do not tell you is that while the study authors compared the number of heart attack admissions in southwest Ireland in the year following the smoking ban with the number of heart attack admissions in the year preceding the smoking ban, they only looked back an additional nine months in order to assess the baseline trend and year-to-year variability in the number of heart attack admissions in this region.
What this means is that there is simply no way to assess whether the observed 14.5% decline in heart attack admissions from 2003 to 2004 was due to the smoking ban or if it was instead due to a pre-existing secular trend in heart attack admissions, or if the change merely reflects underlying variability in the data.
In order to establish the baseline trend in heart attack admissions over time and to assess the degree of year-to-year variability in heart attack admissions, one would need to go back in time much more than simply nine months. Otherwise, these data are virtually meaningless.
For example, the study reports that there were 1277 admissions in 2003 and 1092 admissions in 2004. Suppose that in 2001 there were also about 1280 admissions. This would be consistent with the conclusion that the smoking ban resulted in a significant decline in heart attacks.
However, suppose that in 2001 there had been 1500 heart attack admissions. Then, it would be clear that a 15% decline in heart attack admissions from one year to the next is a common occurrence and that it could not be inferred that the 15% decline from 2003 to 2004 was attributable to the smoking ban.
Complicating matters is the fact that the authors found no decline in heart attack admissions from 2004 to 2005, despite the continued presence of the smoking ban.
In fact, it turns out that there is a secular trend of sharply declining heart attack mortality in Ireland. While this doesn’t necessarily mean that heart attack incidence is declining, it does suggest that there may have been a trend of declining heart attacks in Ireland even before the smoking ban went into effect.
Cardiovascular disease mortality in Ireland has in fact been falling rapidly. Over the past 15 years, it has declined by about half. Some of this decline is due to decreased heart attack incidence. And some of that reduced incidence is due to a drop in smoking rates. All of this happened, of course, before the smoking ban went into effect.
Ischemic heart disease mortality in Ireland decreased by 8.6% in 2003, the year immediately preceding the smoking ban. In 2004, ischemic heart disease mortality declined by only 1.8%.
Does this mean that the smoking ban resulted in an increased rate of death from heart attacks than would have been expected? Of course not. You can’t simply look at a change from one year to the next and attribute it to the smoking ban. You have to carefully examine long-term secular trends, variability in the data, and other factors that affect cardiovascular disease rates.
These problems, however, did not seem to stop the authors of this study from drawing a sweeping conclusion that is completely unjustified by the data which they report. This seems to be par for the course in the tobacco control movement right now. Junk science is passing for perfectly valid science in tobacco control these days.
It will be interesting to see how long it takes for the anti-smoking groups to catch wind of these data and to start spreading these junk science claims widely to the public and policy makers. My guess: it will take only as long as it takes for secondhand smoke exposure to cause hardening of the arteries.