BMC Public Health 2007, 7:21 http://www.biomedcentral.com/1471-2458/7/21 adolescent and both of his/her parents. The index was cre- ated using canonical principal component analysis (CAPCTA) [17], the nonparametric version of the princi- pal component analysis, which has to be used when vari- ables are either multinomial or ordinal. In a density plot the distribution of the acculturation index showed two clearly separated groups (see Figure 1.). Based on visual inspection, the index was dichotomized at 0.6 into high and low acculturation. The components of the accultura- tion index together with the categories of the accultura- tion index are presented in Table 1. The high acculturation Latino group was US born, bi-lingual and most of the interviews were conducted in English. The low accultura- tion Latino group was characterized by youth being for- eign born and more frequent use of Spanish only. Other variables used in the analysis Support provided by adults at school and at home was each measured with 8 items assessing the presence of adults who cared about, listened to and encouraged the adolescent respondent. Using CAPCTA, these variables were combined into two separates scores which were dichotomized at the median into low and high categories. The correlation between the support variables was below 0.4. Additionally we included in the analysis: age of the adolescent (in three groups 12–13, 14–15, 16–17), gen- der, socio-economic status (<200% poverty level and ≥ 200% poverty level), and household type (two parent or one parent household). Statistical analysis Factor analysis was conducted to confirm identical factor structure of the CES-D scale for all subgroups. Internal reliability of the scale was tested by Cronbach's alpha. Univariate analysis was performed by tabulation and chi- square tests between Non-Latino White and Latino ado- lescents with high or low level of acculturation. We used the conventional significance level (p < 0.05). Univariate und multivariate logistic regression was used for the anal- ysis of association between the risk of depressive symp- toms and other variables. Multicollinearity test was performed based on the tolerance coefficient – no colline- Table 1: Ethnic, language and immigration characteristics by acculturation index Non-Hispanic White Latino (high acculturation) Latino (low acculturation) Characteristics Country of birth US Other Citizenship Native Naturalized Other Living in the US Born in the US 10 or more years 5 – 9 years 2 – 4 years 1 or less years Language at home English English + other language Spanish Interview language English Spanish Citizenship and immigration status of mother Native Naturalized Other Citizenship and immigration status of Father Native Naturalized Other N = 2,071 % 96.9 3.1 96.9 1.8 1.3 96.9 1.4 0.9 0.5 0.3 85.6 13.2 1.2 99.7 0.3 88.6 7.3 4.2 89.3 6.7 4.0 N = 865 % 99.5 0.5 99.5 0.5 99.5 0.5 24.3 67.2 8.6 87.4 12.6 39.3 23.4 37.3 34.5 26.9 38.6 N = 260 % 100 20.8 79.2 43.5 25.0 22.7 8.8 1.5 69.6 28.8 47.3 52.7 1.9 5.8 92.3 3.8 14.6 81.5 Page 3 of 9 (page number not for citation purposes)