Objectives: The version of the Minnesota Nicotine Withdrawal Scale (MNWS) under consideration consists of nine items. No psychometric analyses of this version have been published. The objectives of this investigation were to perform a factor analysis and to further assess the psychometric properties of the MNWS.
Research design and methods: Data came from three Phase II clinical trials on varenicline, developed for smoking cessation, in a sample of smokers. Exploratory factor analysis was used to examine the structure of the MNWS in the first completed study (n = 626) over various time periods. The postulated factor structure was then tested in a set of confirmatory analyses conducted on two subsequent studies (n = 627, n = 312). The proposed structure was further evaluated through construct validity and reliability analyses.
Main outcome measures: The nine items of the MNWS included the following: urge to smoke (craving); depressed mood; irritability, frustration, or anger; anxiety; difficulty concentrating; restlessness; increased appetite; difficulty going to sleep; and difficulty staying asleep. Each item was rated by a subject on an ordinal scale from 0 (not at all) to 4 (extreme).
Results: Scree plots and rotated factor patterns from the exploratory factor analyses revealed two multi-item domains--Negative Affect with four items and Insomnia with two items--and three individual items (Craving, Restlessness, Increased Appetite). Confirmatory factor analyses supported the structure with fit indexes exceeding 0.90. The multidimensional framework of the MNWS correlated as expected with health status, depicted an expected course of withdrawal symptoms over time, predicted the sensitivity of withdrawal symptoms on subsequent cessation, and produced internal reliability estimates above 0.70.
Conclusions: Evidence is obtained to support the validity and reliability of the multidimensional structure of the nine-item MNWS. The data suggest that the MNWS has individual constructs on Negative Affect (depressed mood; irritability, frustration, or anger; anxiety; difficulty concentrating), Insomnia (difficulty going to sleep; difficulty staying asleep), Craving, Restlessness, and Increased Appetite. As such, analyzing each construct separately would strengthen the analysis of the popular MNWS.