title: Correlates of digit bias in self-reporting of cigarette per day (CPD) frequency: results from Global Adult Tobacco Survey (GATS), India and its implications.
abstract: BACKGROUND
  Cigarette per day (CPD) use is a key smoking behaviour indicator. It reflects smoking intensity which is directly proportional to the occurrence of tobacco induced cancers. Self reported CPD assessment in surveys may suffer from digit bias and under reporting. Estimates from such surveys could influence the policy decision for tobacco control efforts. In this context, this study aimed at identifying underlying factors of digit bias and its implications for Global Adult Tobacco Surveillance. MATERIALS OR METHODS: Daily manufactured cigarette users CPD frequencies from Global Adult Tobacco Survey (GATS)--India data were analyzed. Adapted Whipple Index was estimated to assess digit bias and data quality of reported CPD frequency. Digit bias was quantified by considering reporting of '0' or '5' as the terminal digits in the CPD frequency. The factors influencing it were identified by bivariate and logistic regression analysis.
  
  
  RESULTS
  The mean and mode of CPD frequency was 6.7 and 10 respectively. Around 14.5%, 15.1% and 15.2% of daily smokers had reported their CPD frequency as 2, 5 and 10 respectively. Modified Whipple index was estimated to be 226.3 indicating poor data quality. Digit bias was observed in 38% of the daily smokers. Heavy smoking, urban residence, North, South, North- East region of India, less than primary, secondary or higher educated and fourth asset index quintile group were significantly associated with digit bias.
  
  
  CONCLUSIONS
  The present study highlighted poor quality of CPD frequency data in the GATS-India survey and need for its improvement. Modeling of digit preference and smoothing of the CPD frequency data is required to improve quality of data. Marketing of 10 cigarette sticks per pack may influence CPD frequency reporting, but this needs further examination. Exploring alternative methods to reduce digit bias in cross sectional surveys should be given priority.
authors.affiliation: Public Health Foundation of India, New Delhi, India. drpratapjena@gmail.com
authors.forename: Pratap Kumar
authors.initials: PK
authors.lastname: Jena
authors.forename: Jugal
authors.initials: J
authors.lastname: Kishore
authors.forename: G
authors.initials: G
authors.lastname: Jahnavi
mesh_terms: D000293:Adolescent; D000328:Adult; D015982:Bias; D003625:Data Collection / Q000592:standards*; D005260:Female; D005500:Follow-Up Studies; D006306:Health Surveys; D006801:Humans; D007194:India / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D057566:Self Report / Q000592:standards*; D012907:Smoking / Q000453:epidemiology*; D014029:Tobacco Use Disorder / Q000517:prevention & control*; D055815:Young Adult