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Baseline adjustment and change revisited: effect of smoking on change in periodontal status following periodontal therapy
Author(s) -
Preus Hans R.,
Sandvik Leiv,
Gjermo Per,
Baelum Vibeke
Publication year - 2014
Publication title -
european journal of oral sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.802
H-Index - 93
eISSN - 1600-0722
pISSN - 0909-8836
DOI - 10.1111/eos.12111
Subject(s) - medicine , periodontitis , analysis of covariance , randomized controlled trial , dentistry , clinical trial , machine learning , computer science
Smokers have frequently been reported to have more severe periodontitis, to respond less favorably to periodontal therapy, and to show elevated rate of recurrence compared with non‐smokers. The aims of this study was to compare the results of baseline‐adjusted and ‐unadjusted analyses when assessing the effect of smoking on change in periodontal status following therapy and to discuss the methodological issues involved. This is a secondary analysis of data from 180 periodontitis patients enrolled in a randomized controlled clinical intervention trial. Information on smoking habits was elicited from the participants before, and 12 months after, therapy. The clinical parameters analyzed were probing pocket depth and clinical attachment level, using both simple analysis of change ( SAC ) and analysis of covariance ( ancova ), adjusting for age, gender, and treatment group. The current smokers presented with more severe periodontitis at baseline than did former and never smokers. Results of the SAC indicated that the current smokers benefitted more from treatment than did former or never smokers, whereas the results of the baseline‐adjusted ancova indicated no such differences. Both sets of results are likely to be biased with respect to valid conclusions regarding the ‘causal’ effect of smoking. Possible sources of bias are discussed.