title: Trajectories of cigarettes per day during the course of telephone tobacco cessation counseling services: a comparison of missing data models.
abstract: BACKGROUND
  Cigarette smoking accounts for approximately 1 in 5 deaths in the United States every year. To combat smoking, a network of telephone-based smoking cessation counseling services or "quitlines" provide smokers in the United States with smoking cessation resources, and several studies have demonstrated the efficacy of quitlines in promoting long-term smoking cessation. Yet, many individuals who enroll in quitlines do not receive all intended calls, and there is a dearth of research on the impact of missing data on the evaluation of quitline outcomes.
  
  
  METHODS
  The current study was a secondary analysis of existing data from a commercial telephone smoking cessation counseling service to estimate the trajectories of cigarettes per day among participants (n = 2,041) during the course of the first 5 calls of the quitline program. Numerous missing data models were estimated to assess the degree to which trajectories of cigarettes per day were associated with the propensity for missing data.
  
  
  RESULTS
  The results from growth curve models indicated a significant decrease in cigarettes per day during the quitline program, which was predicted from levels of nicotine dependence. The comparison of missing data models indicated that the propensity for missing data was not systematically associated with the trajectories of cigarettes per day after controlling for level of nicotine dependence.
  
  
  CONCLUSIONS
  Analyses conducted in the current study provide evidence that the quitline program was effective at reducing cigarettes per day. Researchers are encouraged to examine missing data mechanisms and control for nicotine dependence in studies of smoking cessation treatment outcomes.
authors.affiliation: Department of Psychology,Washington State University, 14204 Northeast Salmon Creek Avenue, Vancouver, WA 98686-9600, USA. katie.witkiewitz@wsu.edu
authors.forename: Katie
authors.initials: K
authors.lastname: Witkiewitz
authors.forename: Terry
authors.initials: T
authors.lastname: Bush
authors.forename: L Brooke
authors.initials: LB
authors.lastname: Magnusson
authors.forename: Beatriz H
authors.initials: BH
authors.lastname: Carlini
authors.forename: Susan M
authors.initials: SM
authors.lastname: Zbikowski
mesh_terms: D000328:Adult; D000368:Aged; D035841:Behavioral Research / Q000458:organization & administration*; D003376:Counseling / Q000379:methods / Q000706:statistics & numerical data*; D003627:Data Interpretation, Statistical; D005260:Female; D006293:Health Promotion / Q000706:statistics & numerical data; D006379:Helping Behavior; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D012044:Regression Analysis; D016540:Smoking Cessation / Q000379:methods / Q000706:statistics & numerical data*; D013689:Telephone / Q000706:statistics & numerical data*; D014029:Tobacco Use Disorder / Q000453:epidemiology / Q000628:therapy*; D016896:Treatment Outcome; D014481:United States / Q000453:epidemiology; D055815:Young Adult