The subjects of the study are '236 male and female smokers who wanted to give up'.
Among those who managed to quit for a while, the researchers found that they were in very high spirits (happy) during the check-ups when their smoking cessation was being successfully carried out. However, after failing their moods darkened significantly, and in many cases to lower depths than before the whole study began.
Kahler said that enhanced mood and periods of abstinence went hand-in-hand – the correlation was clear.
[...]
Kahler believes it is possible to extrapolate from this study and generalize over the whole population, even though his participants were relatively heavy drinkers. He refers to a 2002 study of smokers who had all experienced episodes of depression in their lives, but did not all drink.
The authors added that the link between happiness and smoking cessation was strong, regardless of whether the participant was drinking less or the same – the constant was successful smoking cessation.Observation: 10 out of 10. Inference: 0 out of 10.