Specifically, the present study examined the prediction of membership in each any other enquiries trajectory in high school from the prior development of sensation seeking, and the relation between trajectory membership and subsequent use of hookah in combination with smoking at age 20/21. Smoking Trajectories in Adolescence Trajectory classes are an efficient way to describe the development of adolescent smoking. Because trajectories are person centered, individuals can be classified into one of several classes based on their growth across the period. Previous studies have found that for those who are already smoking at entry into high school, trajectory classes differ on level and steepness of escalation. For those who start high school as nonsmokers, classes differ on early or later onset and subsequent steepness of escalation.

Most studies across adolescence and emerging adulthood have identified three to six distinct classes, including nonsmokers. For example, Abroms, Simons-Morton, Haynie, and Chen (2005) found five trajectory classes describing the development of smoking from middle school to the first year of high school (6th�C9th grade). In their study from 6th/7th grade to 10th/11th grade, Colder et al. (2001) identified five classes in addition to Stable Nonsmokers. Guo et al. (2002) also found five trajectory classes across ages 13�C18 years. Recently, Heron, Hickman, Macleod, and Munaf�� (2011) identified three distinct patterns of smoking initiation from ages 14 to 16 years: experimenters, late-onset regular smokers, and early-onset regular smokers.

Trajectory classes that show decline or quitting are more likely to be found in studies encompassing longer time spans (Brook, Balka, Ning, & Brook, 2007; Brook et al., 2008; Brook, Ning, & Brook, 2006; Chassin, Presson, Pitts, & Sherman, 2000; Orlando, Tucker, Ellickson, & Klein, 2005; White, Pandina, & Chen, 2002). Sensation Seeking as an Etiological Variable Sensation seeking is the tendency to seek out experiences and situations that are novel, exciting, or rewarding. An examination of change across development indicates a curvilinear pattern: sensation seeking typically increases during childhood and early adolescence but then levels off and declines in late adolescence and adulthood (Harden Drug_discovery & Tucker-Drob, 2011; Steinberg et al., 2008; Zuckerman, Eysenck, & Eysenck, 1978). Novel experiences are highly rewarding for sensation seekers, and risky behavior such as substance use is one way to obtain such rewards (Roberti, 2004; Steinberg et al., 2008; Zuckerman, 1996). Sensation seeking, treated as a stable trait, has been associated with underage cigarette smoking in numerous cross-sectional and prospective studies (e.g.