The primary sampling United States Youth Risk Behavior Survey (YRBS) of 2005 comprised all schools (public and private) with students in at least one of grades 9–12 in the 50 states and the District of Columbia. The sampling frame was obtained from the Quality Education Data (QED), Inc. database [11
]. This database is one of the most comprehensive on the status of all schools in the United States. It includes information on both public and private schools and the most recent data from the Common Core of Data from the National Center for Education Statistics [12
A three-stage cluster sample design was used to obtain a nationally representative sample of students in grades 9–12. In the first-stage of sampling, 1,261 primary sampling units (PSUs), consisting of counties, subareas of large counties, or groups of smaller, adjacent counties were obtained. The 1,261 PSUs were categorized into 16 strata according to their metropolitan statistical area (MSA) status. From these 1,261 PSUs, 57 were selected with probability proportional to overall school enrollment size for the PSU. In the second stage of sampling, a total of 203 schools with any of grades 9–12 were selected with probability proportional to school enrollment size. The third stage of sampling consisted of randomly selecting, in each chosen school and in each of grades 9–12, one or two classrooms from either a required subject or a required period (e.g., homeroom or second period).
All students in selected classes were eligible to participate. There was no replacement of schools, classes, or students that refused to participate. Black and Hispanic students were oversampled in order to allow for stratified analysis of these groups. The sampling of these groups provided that: 1) larger sampling rates were used to select PSUs that are in high-black and high-Hispanic strata; 2) a modified measure of size was used that increased the probability of selecting schools with a disproportionately high minority enrollment; and 3) two classes per grade, rather than one, were selected in schools with a high minority enrollment. A weight based on student sex, race/ethnicity, and grade level was applied to each record to adjust for school and student non-response and oversampling of black and Hispanic students. The overall weights were scaled so that the weighted count of students equals the total sample size, and the weighted proportions of students in each grade match the national population proportions. For the 2005 national YRBS, 13,953 questionnaires were completed in 159 schools. The school response rate was 78%, and the student response rate was 86%. The school response rate multiplied by the student response rate produced an overall response rate of 67%. CDC's Institutional Review Board granted clearance for the national YRBS.
Data Collection and Questionnaire design
Study participants completed the questionnaires anonymously within a class period. Student completed the questionnaires on computer scannable booklet or answer sheet.
Local parental permission procedures were followed before questionnaire administration. These procedures differed from state to state and from school district to school district.
The core questionnaire had 87 questions. States and cities were free to add or delete any questions for whatever reasons. Information about the reliability of the core questionnaire is published elsewhere [13
To assess physical fighting, participants were asked the following question: "During the past 12 months, how many times were you in a physical fight on school property? (0 times, 1 time, 2 or 3 times, 4 or 5 times, 6 or 7 times, 8 or 9 times, 10 or 11 times, 12 or more times). During the analysis, in both Univariate and Multivariate, we recorded "0 times" as "no" and "1 or more times" as "yes". Current cigarette smoking meant having smoked cigarettes one or more days in the last 30 days. Alcohol use was defined as having had at least one drink of alcohol one day or more in the last 30 days while illicit drug use meant having ever used any of the following: marijuana, any form of cocaine, glue, heroin, methamphetamines, ecstasy, and steroid pills or shots.
Data analysis was only conducted for complete questionnaires. Our analysis is restricted to students in high school (elementary school excluded). As per requirement of the Office of Management and Budget of the US government, race/ethnicity categorization followed from the following questions and responses:
from two question: 1) "Are you Hispanic or Latino?" (options were "yes" or "no"), and 2) "What is your race?" (options were "American Indian or Alaska Native," "Asian," "Black or African American," "Native Hawaiian or Other Pacific Islander," or "White"). For the second question, students could select more than one response option. For this report, students were classified as "Hispanic" if they answered "yes" to the first question, regardless of how they answered the second question. Students were classified as "Black" if they answered "no" to the first question and selected only "Black or African American" to the second question. Students were classified as "White" if they answered "no" to the first question and selected only "White" to the second question. Students were classified as "other" if they answered "no" to the first question and selected "American Indian or Alaska Native," "Asian," and/or "Native Hawaiian or Other Pacific Islander" or selected more than one response to the second question.
For the 2005 state and local YRBS, race/ethnicity was computed from one question: "How do you describe yourself?" (response options were "American Indian or Alaska Native," "Asian," "Black or African American," "Hispanic or Latino," "Native Hawaiian or Other Pacific Islander," or "White"). Students could select more than one response option. For this report, students were classified as "Hispanic" if they selected "Hispanic or Latino" only or if they selected "Hispanic or Latino" plus any other response option. Students were classified as "Black" if they selected "Black or African-American" only. Students were classified as "White" if they selected "White" only. Students were classified as "other" in the recoding if they selected "American Indian or Alaska Native" only, "Asian" only, and/or "Native Hawaiian or Other Pacific Islander" only or multiple response options except "Hispanic or Latino."
Data were analyzed using SAS software version 9.0.3 (SAS, Cary, North Carolina, United States). We obtained frequencies and proportions of relevant variables. We also assess associations using multivariate logistic regression analysis with having engaging in a physical fight as the outcome. The variables assessed for association were those that have previously been reported in previous studies [14
]. Bivariate analysis results report unadjusted effect estimates while multivariate analysis reports effect estimates following control of co-variates.