Yost et al. BMC Public Health 2010, 10:465 http://www.biomedcentral.com/1471-2458/10/465 lose weight. Lastly, among demographic variables in a sample of female adolescents from five major U.S. cities, researchers found no evidence of a relationship between SES (as measured by parental education) and trying to control or lose weight [21]. Previous study findings indicate BMI and weight per- ception are associated with obese and overweight ado- lescents’ efforts to lose weight. Researchers report that a significant positive association exists between trying to lose weight and BMI among adolescents in the United States and internationally [20,22,23,27,28]. Furthermore, findings indicate that obese female adolescents are sig- nificantly more likely to be trying to lose weight than overweight female adolescents [22]. Researchers also report that a relatively large percentage of U.S. adoles- cents who perceive themselves as overweight are trying to lose weight (70.3%) [26], with greater percentages of White/non-Hispanic White adolescent females who per- ceive themselves as “too fat” trying to lose weight, com- pared to Hispanic and Black/African American adolescents [16]. These data and associations are lim- ited, however, as the only significant positive association between weight perception and trying to lose weight was reported among a sample of adolescents in Beirut, Lebanon [23]. However, again, the finding is limited due to its lack of generalizability. Studies present conflicting data on whether U.S. ado- lescent females are significantly more likely [11,26,29] or less likely [15,25] than U.S. adolescent males to exercise as a means to control and/or lose weight. Nevertheless, study findings indicate exercise is the most common behaviour among U.S. and international female adoles- cents trying to control or lose weight [22,28]. Research- ers also report that African American [15,25] and Hispanic [25] female adolescents in the United States are significantly less likely to exercise than their White counterparts. Although no studies have considered the association between adolescents’ weight perception and engaging in exercise to trying to lose weight, researchers report a significant positive relationship between BMI and engaging in exercise to trying to lose weight among U.S. female adolescents [25]. Thus, based on findings reported in the literature, female adolescents are more likely than male adoles- cents to be trying to lose weight and are most likely to engage in exercise to do so. However, limited evidence demonstrates associations between demographic vari- ables, BMI, and weight perception among female adoles- cents trying to lose weight. Furthermore, previous studies have not examined the association of the accu- racy of female adolescents’ weight perception with their efforts to lose weight. To fill this gap in the literature, the current study focused on identifying whether BMI and weight perception are associated with trying to lose Page 3 of 11 weight and engaging in exercise as a weight-loss method among U.S. female adolescents. This study addressed the following research questions: (a) Are BMI and weight perception associated with trying to lose weight among female adolescents, controlling for age, race/eth- nicity, and SES?; and (b) Are BMI, weight perception, and trying to lose weight associated with female adoles- cents’ report of engaging in exercise as a weight-loss method, controlling for age, race/ethnicity, and SES? Methods Design The current study was a nonexperimental, descriptive, comparatory secondary analysis of data from the National Longitudinal Study of Adolescent Health [30]. n.d.a). Add Health was a longitudinal, school-based study that collected data on a variety of health-related behaviours in a nationally representative sample of U.S. adolescents in grades 7 through 12. Using a multistage, stratified, school-based cluster sampling design, Add Health subjects were first enrolled during the adminis- tration of an in-school questionnaire in 1994 (Wave I, Stage 1). One year later, additional subjects from school rosters were enrolled during in-home interviews (Wave 1, Stage 2; N = 20,745). Add Health subjects were subse- quently followed over time during in-home interviews 2 and 6 years later: Wave II (1996; N = 14,738) and Wave III (2000; N = 15,170) [30]. Sample for the Present Study The present study included females aged 13 to 18 years old on whom data were collected during in-home inter- views at Wave I and Wave II of the Add Health study. Female subjects were excluded if they (a) were not included in the core sample; (b) were younger than 13 years or older than 18 years at Wave II; (c) were missing data for age, race/ethnicity, or SES; (d) reported pregnancy at Wave II; and (e) were determined to be physically disabled during data collected at Wave II. The Add Health public-use data set provides data for more than 2,000 female adolescents at Wave II who met inclusion criteria. Due to the large sample available for the present study, a power analysis was deemed unne- cessary upon statistical consultation. Data Collection Data for the present study were obtained from data col- lected from the Add Health study. From April to August 1996, highly structured in-home interviews were conducted by trained interviewers using computer- assisted self-interview for Add Health Wave II data col- lection [31]. All measures were self-reported, except for height and weight, which were measured by the trained interviewers immediately following the interview.