Limitations
chronic obstructive pulmonary disease, psychiatric
CHRONIC OBSTRUCTIVE PULMONARY DISEASE, DISORDERS
Although the instrument of the randomized treatment group is theoretically sound, the instrument was not robust in this data set. Given the low likelihood of detecting an association of the size we observed in the observational data with the IV analysis with our sample size, future work would need a larger sample size. Our results, therefore, do not exclude a causal relationship between smoking cessation and improved mental health for people with and without psychiatric disorders.This study had substantial loss to follow-up, which is common in smoking cessation trials. Evidence suggests that those who fail to attend follow-up are more likely to continue smoking.The EAGLES trialLike many other smoking cessation studies, this study classified people who did not meet the strict definition of abstinence as continuing smoking. Those people who had achieved abstinence but not had 15 weeks of abstinence may have experienced changes in their mental health similar to those who met the 15-week abstinence, as the evidence suggests that the association is of similar strength in people with only 6 weeks of abstinence after several years.Although participants with and without a psychiatric history showed reduced HADS scores, these were less than the minimally clinically important differences suggested by populations with chronic obstructive pulmonary disease and CVD.The EAGLES trial