Original articles
Comparing Participants and Nonparticipants in a Smoking Cessation Trial: Selection Factors Associated With General Practitioner Recruitment Activity

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Abstract

We studied the relationship between smokers’ sociodemographic characteristics, their smoking habit, health status, and the probability of their having been approached for recruitment in the smoking cessation trial performed in Turin, Italy, with the aim of gathering information on the role of selection criteria adopted by general practitioners (GPs) in offering anti-smoking counseling. The 965 smokers who were offered participation in the trial were matched to a sample of eligible smokers (n = 277), selected from the rosters of the 42 GPs collaborating in the trial, who had not been invited to participate. The probability of being offered enrollment, estimated through a multiple conditional logistic regression model, assuming the GP as the matching variable, was significantly increased for intermediate (10–19 cigarettes per day: odds ratio [OR] = 4.13; 95% confidence interval [CI]: 2.63–6.47) and heavy (20 cigarettes per day or more: OR = 10.12; 95% CI: 6.51–15.75) smokers, for smokers diagnosed with chronic cardiovascular (OR = 2.06; 95% CI: 1.19–3.58), or respiratory (OR = 2.50; 95% CI: 1.40–4.48) diseases, and for smokers mentioning an intermediate number (2–4) of past quit attempts (OR = 3.70; 95% CI: 2.18–6.28). General Practitioners focused their recruitment activity on higer-risk smokers or smokers who had tried to quit, to offer more clues for intervention. Assessing the potential public health benefit of preventive interventions requires a more systematic evaluation of the generalizability of the reported findings.

Introduction

Various reports 1, 2, 3, 4 suggested that smokers’ characteristics influence their likelihood of being offered smoking cessation advice in the context of routine clinical activity.

Physicians apparently focus on the smokers they perceive to be at increased risk of ill health effects of cigarettes. Previous diagnoses of smoking related diseases 1, 2, 3, 4 higher levels of tobacco consumption 1, 3, and age [3] emerged as important predictors of counseling. Smokers reporting several attempts to quit in the past [4] or a longer duration of smoking habit 1, 4, as well as those reporting a higher level of attendance at a doctor’s office 1, 2, 3, were more likely to have been told to stop.

It has been suggested [5] that this kind of selective counseling practice be maintained when recruiting smokers for intervention studies. The differential decline of the effectiveness rate, observed across physicians participating in a cessation trial [5], was ascribed to an increased selectivity in delivering counseling. Indeed, some physicians not only counseled patients less often but also adopted more restrictive criteria than indicated in the study protocol, recruiting subjects with symptoms of pulmonary disease, or heavy smokers. Although the low number (n = 4) of physicians involved in the study [5] limits the strength of this conclusion, the reported findings suggest that the generalizability of the results of smoking cessation trials in general practice might be hampered by the persistent tendency among general practitioners (GPs) to target high-risk smokers.

The introduction of unplanned selection criteria could affect the external validity of the observed results, thus impairing their application to clinical practice. Indeed, impact assessments of such interventions are based on the assumption that GPs can take the opportunity of office visits to offer their support for quit attempts to all smokers, regardless of their health status or level of addiction.

The role of selective criteria adopted by some GPs in offering antismoking advice was explored by analyzing the relationship of smokers’ sociodemographic characteristics, smoking habits, and health status to their probability of having been offered recruitment in a smoking cessation trial.

Section snippets

Materials and methods

We conducted a case-control study, comparing smokers who were offered participation in a smoking cessation trial performed in Turin [6] to a matched sample of smokers, potentially eligible for recruitment but not invited to participate, who were selected from the rosters of the GPs collaborating in the trial.

Results

Seven hundred ninety-nine (90.6%) of the 882 smokers recruited in the cessation trial who were considered eligible cases for this case-control study answered the phone interview administered at recruitment. Seven hundred sixty-five (86.7%) completed the 12-month follow-up questionnaire. Both questionnaires were available for 709 (80.4%) smokers. Of the 83 smokers refusing to participate in the trial who were considered as eligible cases for this study, 53 (63.9%) agreed to be contacted for the

Discussion

Comparability of subjects actually entered into a trial to those who were not randomized, with respect to their susceptibility to the outcome studied, is a crucial aspect influencing external validity of the trial results. A higher participation rate of married, employed, or better-educated subjects, among those who were eligible for recruitment, has been documented in large prevention trials 13, 14, 15. Our analysis showed that eligible, albeit not recruited, smokers differed from those

Acknowledgements

The present study was funded by the USL TORINO I (Turin Health District 1); C.S. was also supported by a fellowship of the Lega Italiana per la Lotta contro i Tumori. The authors are grateful to Dr. S. Suissa for his input in the preliminary phase of the analysis, and to Drs. K.S. Joseph and M.J. Hodge for their helpful comments on earlier drafts of the article. The authors gratefully acknowledge the support of SIMG (Societa’ Italiana di Medicina Generale), as well as the advice of Drs. G.

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