Table 1.

Factor loadings for Nicotine Dependence Syndrome Scale items included in measure of overall nicotine dependence severity

Symptom	Included in severity measure (yes/no)	Factor loading:
After not smoking for a while, you need to smoke in order to feel less restless and irritable	Yes	0.60
When you don’t smoke for a few hours, you start to crave cigarettes	Yes	0.72
You sometimes have strong cravings for a cigarette where it feels like you’re in the grip of a force you can’t control	Yes	0.56
You feel a sense of control over your smoking – that is, you can “take it or leave it” at any time	No ^a
You tend to avoid places that don’t allow smoking, even if you would otherwise enjoy them.	Yes	0.35
Do you have any friends who do not smoke cigarettes?	No ^b	---
There are times when you choose not to be around your friends who don’t smoke because they won’t like it if you smoke	No ^b	---
Even if you are traveling a long distance, you would rather not travel by airplane because you would not be allowed to smoke	Yes	0.35
You sometimes worry that you will run out of cigarettes	Yes	0.62
You smoke cigarettes fairly regularly throughout the day	Yes	0.72
You smoke about the same amount on weekends as on weekdays	No ^c	---
You smoke just about the same number of cigarettes from day to day	Yes	0.59
It’s hard for you to say how many cigarettes you smoke per day because the number often changes	No ^a	---
It’s normal for you to smoke several cigarettes in an hour, then not have another one until hours later	Yes	0.32
The number of cigarettes you smoke per day is often influenced by other things – how you are feeling, or what you are doing for example	No ^c	---
Your smoking is not affected much by other things. For example, you smoke about the same amount whether you’re relaxing or working, happy or sad, alone or with others	No ^a	---
Since you started smoking, the amount you smoke has increased	Yes	0.64
Compared to when you first started smoking, you need to smoke a lot more now in order to be satisfied	Yes	0.68
Compared to when you first started smoking, you can smoke much, much more now before you start to feel anything	Yes	0.53

Not included because of low factor loading (< 0.30)

Not included because skip pattern resulted in missing data for a portion of smokers

A similar symptom was included in the final measure