Expected number of quit attempts prior to quitting successfully | |||||
---|---|---|---|---|---|
Method | Key assumption | Expected direction of bias | Overall (n=1277) | Daily (n=1092) | Occasional (n=185) |
Method 1 | |||||
Recalled quit attempts, among successful quitters | Recall of quit attempts over a lifetime is valid. Only successful quitters are included | Underestimate: only includes successful quitters, recall over a lifetime is poor | 6.3 | 6.8 | 4.7 |
Method 2 | |||||
Constant rate assumption | Every quit attempt has the same chance of success, no matter how many previous quit attempts there have been | Underestimate: chance of success decreases by number of previous quit attempts | 19.6 | 20.4 | 16.7 |
Method 3 | |||||
Life table, observed quit success rates | The success rate of quit attempts varies by ‘quit attempt age’, as observed during the period of the study | Offsetting: overestimates chance of success on quit attempt, may underestimate on subsequent attempts | 29.6 | 29.5 | 11.4 |
Method 4 | |||||
Life table, recalled lifetime quit numbers | The success rate of quit attempts varies by ‘quit attempt age’, as observed and recalled | Probable overestimate: recall over a lifetime is underestimated, but calculation does not include successful quitters who had quit prior to the study | 142.0 | 142.3 | 21.0 |
Successful quit attempts were measured as abstinence of 1 year or longer.