Correlates of Digit Bias in Self-reporting of Cigarette per Day (CPD) Frequency: Results from Global Adult Tobacco Survey (GATS), India and its Implications


Background: Cigarette per day (CPD) use is a key smoking behaviour indicator. It reflects smoking intensitywhich is directly proportional to the occurrence of tobacco induced cancers. Self reported CPD assessment insurveys may suffer from digit bias and under reporting. Estimates from such surveys could influence the policydecision for tobacco control efforts. In this context, this study aimed at identifying underlying factors of digit biasand its implications for Global Adult Tobacco Surveillance. Materials or
Methods: Daily manufactured cigaretteusers CPD frequencies from Global Adult Tobacco Survey (GATS) - India data were analyzed. Adapted WhippleIndex was estimated to assess digit bias and data quality of reported CPD frequency. Digit bias was quantifiedby considering reporting of ‘0’ or ‘5’ as the terminal digits in the CPD frequency. The factors influencing it wereidentified by bivariate and logistic regression analysis.
Results: The mean and mode of CPD frequency was 6.7and 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 biaswas observed in 38% of the daily smokers. Heavy smoking, urban residence, North, South, North- East region ofIndia, less than primary, secondary or higher educated and fourth asset index quintile group were significantlyassociated with digit bias. Discussion: The present study highlighted poor quality of CPD frequency data inthe GATS-India survey and need for its improvement. Modeling of digit preference and smoothing of the CPDfrequency data is required to improve quality of data. Marketing of 10 cigarette sticks per pack may influenceCPD frequency reporting, but this needs further examination. Exploring alternative methods to reduce digitbias in cross sectional surveys should be given priority