Table 3

Estimate of the number of quit attempts made prior to successfully quitting for 1 year or longer among 1277 smokers in the Ontario Tobacco Survey for four different methods of calculation

Expected number of quit attempts prior to quitting successfully
MethodKey assumptionExpected direction of biasOverall (n=1277)Daily (n=1092)Occasional (n=185)
Method 1
 Recalled quit attempts, among successful quittersRecall of quit attempts over a lifetime is valid. Only successful quitters are includedUnderestimate: only includes successful quitters, recall over a lifetime is poor6.36.84.7
Method 2
 Constant rate assumptionEvery quit attempt has the same chance of success, no matter how many previous quit attempts there have beenUnderestimate: chance of success decreases by number of previous quit attempts19.620.416.7
Method 3
 Life table, observed quit success ratesThe success rate of quit attempts varies by ‘quit attempt age’, as observed during the period of the studyOffsetting: overestimates chance of success on quit attempt, may underestimate on subsequent attempts29.629.511.4
Method 4
 Life table, recalled lifetime quit numbersThe success rate of quit attempts varies by ‘quit attempt age’, as observed and recalledProbable overestimate: recall over a lifetime is underestimated, but calculation does not include successful quitters who had quit prior to the study142.0142.321.0
  • Successful quit attempts were measured as abstinence of 1 year or longer.