The five items that did not exhibit increased endorsements are (dotted lines in Figure 2): need more to be satisfied; smoke to relieve feelings; smoke to keep from discomfort; grip of unknown force when craving; worth smoking in cold or rain. Figure 2. NDSS item change (first logits) over time. Discussion In this article, we described IRT and mixed models in the examination of the characteristics selleck kinase inhibitor and development of the 10 items of the NDSS scale among a sample of adolescents. While a typical mixed-effects regression model applied to the item-averaged NDSS score revealed linear increase in nicotine dependence among adolescents, the IRT models with item intercept and discrimination parameters revealed more item-level information.

By and large, the item discrimination values were inversely related to the intercepts (which are minus the product of discriminations and difficulties in the IRT parameterization), indicating that the less frequently endorsed items were better able to distinguish higher levels of dependency. We found that items 5 (function better after morning cigarette), 8 (find cigarette in rainstorm), and 10 (choose to spend money on cigarettes than lunch) fell into this category. In addition, these three items had the most profound increases over time. Two of these items reflect the total score dimension of the original NDSS (Shiffman, Waters, & Hickcox, 2004), and the third reflects more of a priority dimension, with adolescents who endorse this item indicating that they are choosing cigarettes over other behavioral reinforcers.

What is perhaps more interesting are items that are relatively frequently endorsed (less negative intercepts), but also more discriminating. Such items would be better able to distinguish relatively low and high levels of dependency. Here, the item, ��It is worth smoking even in cold or rainy weather,�� is best for this purpose. Notice, however, the endorsement level of this item remained stable over time, that is, there was no significant change over time for this item. An item that did exhibit significant increase over time was an ��easy,�� or frequently endorsed item, Item 2 (increased smoking). There was also an increase in the endorsement of Item 6 over time (Whenever I go without a smoke for a few hours, I experience craving), whose difficulty and discrimination values were both in the middle range.

Together, the items that changed significantly over time reflected the general drive concept of dependence, as well as the total first overarching dimension of dependence Dacomitinib (c.f., Costello, Dierker, Sledjeski, Flaherty, Flay, & Shiffman, 2007). The drive dimension reflects the individual��s compulsion to smoke or subjective need for nicotine, often in response to the need to relieve withdrawal symptoms (Shiffman, Waters, & Hickcox, 2004).