International Journal of Epidemiology
IJE Advance Access published on January 17, 2007.

Stanton A Glantz

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.1 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...

Analyses need reliable unbiased data to support reliable conclusions and avoid the placebo effect. It will be interesting to see if Adda et al.’s1 conclusions still hold when the objective tax data become available or, if as one Philip Morris Tobacco Company lobbyist observed in 1994 when talking to her fellow lobbyists, ‘economic arguments often used by the [tobacco] industry to scare off smoking ban activity were no longer working, if indeed they ever did. These arguments simply had no credibility with the public, which isn’t surprising when you consider our dire predictions in the past rarely came true.’12

Referenced IJE study: [NIMI 5-1-07]

Short-run economic effects of the Scottish smoking ban

Source: IJE