Commentary: Assessing the effects of the Scottish Smokefree Law—the placebo effect and the importance of obtaining unbiased data

The placebo effect, when patients report feeling better after receiving a treatment even though the treatment has no real benefit, is a well-known pitfall in clinical trials. To avoid reporting misleading or incorrect results in trials, when possible investigators blind the subjects to the treatment and seek objective measures of outcome that are unaffected by the experimental subjects’ beliefs. The need for objective outcome measures is particularly important when it is not possible to blind the experimental subjects. The paper by Adda et al. of perceived effects of the Scottish smokefree law in this issue of IJE is a textbook example of the placebo effect and how collecting subjective data can lead to unreliable conclusions. Adda et al. used a quasi-experimental design in which they compared reported changes in pub business in Scotland a month or so after the law went into effect with changes reported across the border in Northern England. Based on data collected in a telephone survey, they report a 10% drop in sales and a 14% decrease in customers in Scotland compared with England. In most cases, a random telephone survey would provide reasonably reliable information for a study such as this. The use of a telephone survey to ask a random sample of pub owners about their business before and after the smokefree law went into effect is, however, very likely to be the subject of serious downward bias in the level of business reported by pub owners after a smoking ban went into effect. Why? The tobacco industry has known since the 1970s that creating smokefree environments was both broadly supported by the public and a serious threat to the industry’s viability. The industry also understood that it had little public credibility, so worked aggressively to develop ‘third parties’, particularly in the hospitality industry to lobby against smoking restrictions. Part of this decades-long effort to mobilize restaurant and pub owners against smoking restrictions was to repeat the claim that smokefree laws cut restaurant and bar revenues, generally around 30%. Not surprisingly, during the debate over the Scottish law, the Scottish Licensed Trade Association predicted that annual profits in licensed premises would drop by £86 million, 2300 jobs would be lost and 142 pubs would close if the law was passed. In addition, the chief executive of the Vintners Federation of Ireland testified that the law there led to a 25% drop in alcohol sales in Ireland. (Like other similar claims made by tobacco industry allies, the claim about Ireland was not borne out by the facts.) The drumbeat of claims by hospitality associations all over the world has had an effect on perceptions of the effects of 100% smokefree laws on people in the hospitality trades and the opinion that revenues will be or were affected in the short run by these laws is widespread. This negative placebo effect is also most likely to be acting soon after the law goes into force, when the tobacco industry—working through third parties—works to create the impression that the law is not working and is creating economic chaos. Thus, it is not surprising that among the 97 economic impact studies of smokefree laws reviewed by Scollo et al., studies that used subjective measures of outcome (such as telephone reported levels of business) were four times more likely to conclude that there was a negative economic effect than studies that used objective measures of impact (such as tax receipts reported to the government) (P1⁄4 0.007). Over time, the anxiety that the tobacco industry and its allies generate subsides and publicans tend to report neutral or positive effects. This is already happening in Scotland. For example, in November 2006 the Guardian reported that ‘Wetherspoon said its 39 Scottish pubs, where a national ban has already come into force, were trading well despite the new smoking laws. Pubs in Scotland increased like-for-like sales by 5.2% in the 3 months to October 29, following the smoking ban there in March.’ Once enough time has passed to get hard data, the initial reports of adverse economic effects prove to have been wrong. The need to wait for the public relations hype to settle down and to use objective verifiable data (such as tax receipt data collected by the government) is why there is a strong consensus that one needs at least one of year of data to assess the actual effects of these laws. Analyses need reliable unbiased data to support reliable conclusions and avoid the placebo effect. It will be interesting to see if Adda et al.’s conclusions still hold when the objective tax data become available or, if as one Philip Morris Tobacco * This work was supported by National Cancer Institute Grant CA-61021. The funding agency had no involvement in the conduct of the research or the preparation or review of the manuscript. University of California, San Francisco, CA 9413-1390, USA. E-mail: glantz@medicine.ucsf.edu Published by Oxford University Press on behalf of the International Epidemiological Association The Author 2007; all rights reserved. Advance Access publication 17 January 2007 International Journal of Epidemiology 2007;36:155–156 doi:10.1093/ije/dyl303