This study utilizes a quasi-experimental pre- and post-test survey design to examine the effects of a course, called HIV/AIDS: Science, Behavior, and Society, on undergraduate students’ HIV knowledge, attitudes and risky sexual behaviors. With the assistance of social work faculty the course incorporates experiential learning pedagogy and a transdisciplinary perspective. Although the course was not designed as a prevention program, the theory of health behavior suggests the incorporation of experiential learning will impact crucial HIV/AIDS attitudes and behaviors. When regression models were applied, relative to the comparison group (N = 111), the HIV/AIDS class students (N = 79) reported an increase in post-test HIV knowledge, perceived susceptibility to HIV among females, and a reduction of risky sexual attitudes among sexually active students.
HIV; AIDS; college students; prevention; risk behavior; theory of health behavior
This study examined whether the efficacy of keepin’ it REAL, a model program for substance use prevention in schools, was moderated by gender, ethnicity, and acculturation. Gender differences in program efficacy may arise through boys’ higher risk of drug use, inadequate attention to girls’ developmental issues, or cultural factors like polarized gender expectations. Data came from a randomized trial in 35 Phoenix, Arizona, middle schools involving 4,622 mostly Latino 7th graders. Using multi-level mixed models and multiple imputation missing techniques, results for the total sample showed no gender differences in program effects on recent substance use, but the program was more effective in fostering boys’ than girls’ anti-drug norms. Subgroup analyses demonstrated several more beneficial program effects for boys than girls (less alcohol and cigarette use and stronger anti-drug norms), but only among less acculturated Latinos. There were no gender differences in program effects among more acculturated Latinos, nor among non-Latino whites.
Understanding how schools—a key context for children—shape students’ cultural trajectories is important since these trajectories are tied to youth development and achievement. This study assessed how the size of the school’s group of acculturated Latino and non-Latino students influenced the acculturation of 1,720 Latino 5th-grade students from urban public schools in the Southwest United States. A longitudinal secondary data analysis revealed that controlling for wave 1 acculturation, youths in schools with larger proportions of linguistically acculturated students were more acculturated at wave 2 than youths in schools with smaller proportions of such students. This effect was independent of Latino students’ baseline acculturation level and was found even in schools with minority proportions of more acculturated students.
This study applies advanced conceptualization and measurement to an analysis of acculturation among 1,632 Mexican-heritage preadolescents. We assessed whether – and how – multiple measures combine to form a latent acculturation construct that groups individuals into classes; and determine how many and what classes (or types) of acculturation are experienced by this sample of 5th graders. Measures included attitudinal, behavioral, and linguistic acculturation, generation status, time in the U.S., ethnic identification, and contact with the culture of origin. The analysis identified five classes of acculturation, differing in size and characterized by specific measures of acculturation: less acculturated, moderately bicultural, strongly bicultural, highly acculturated, and marginalized. Although most youths fell into the first four classes, consonant with their exposure to American society, a small minority of youths fell into the last class. Despite substantial exposure to U.S. culture and recent exposure to Mexican culture, these youth showed little affinity for either culture.
acculturation; preadolescents; Mexican
This article examined the impact of linguistic acculturation and gender on the substance use initiation of a sample of 1,473 Mexican heritage preadolescents attending 30 public schools in Phoenix, Arizona. It was hypothesized that linguistic acculturation operates differently as a risk or protective factor for young children than for older youth. The study used discrete-time event history methods to model the rate at which nonusing children initiate substance use. Alcohol, cigarettes, marijuana, and inhalants were studied separately while inhalant use was examined more closely. Results suggested that while linguistic acculturation is a risk factor for Mexican heritage preadolescents, this association depended on gender, the linguistic acculturation context (family, friends, or media), and the type of substance. For inhalants, higher linguistic acculturation with friends was inversely associated with drug initiation both for boys and girls. Implications for preventive science and future intervention research are discussed.
acculturation; bilingual/bicultural; Hispanic/Latino/Latina; substance use/alcohol and drug use
This article presents the findings of a study exploring two questions: What age is most efficacious to expose Mexican heritage youth to drug abuse prevention interventions, and what dosage of the prevention intervention is needed? These issues are relevant to Mexican heritage youth—many from immigrant families—in particular ways due to the acculturation process and other contextual factors. The study utilized growth curve modeling to investigate the trajectory of recent substance use (alcohol, cigarettes, marijuana, inhalants) among Mexican heritage students (N = 1,670) participating in the keepin’ it REAL drug prevention program at different developmental periods: the elementary school (5th grade), middle school (7th grade), or both. The findings provide no evidence that intervening only in elementary school was effective in altering substance use trajectories from 5th to 8th grade, either for licit nor illicit substances. Implementing keepin’ it REAL in middle school alone altered the trajectories of use of all four substances for Mexican heritage youth. A double dose of prevention, in elementary and middle school proved to be equally as effective as intervening in 7th grade only, and only for marijuana and inhalants. The decrease in use of marijuana and inhalants among students in the 7th-grade-only or the 5th- and 7th-grade interventions occurred just after students received the curriculum intervention in 7th grade. These results are interpreted from an ecodevelopmental and culturally specific perspective and recommendations for prevention and future research are discussed.
Substance use prevention; Early intervention; Mexican Americans; Preadolescents; Adolescents
Despite elevated levels of substance use among many Latino youths, there has been little research on protective factors against such use. In keeping with federal commitments to address health disparities, this prospective study examined the protective influence of religion on substance use among a school-based sample (N = 804) of youths of Mexican heritage in the American Southwest. Drawing from the social capital literature, the authors posited that both integration into religious networks and trust in religious values at time 1 (Tl) would predict less likelihood of using substances at time 2 (T2) but that exposure to religious norms at Tl would not predict subsequent substance use at T2. The hypotheses regarding religious networks and religious norms were largely confirmed, whereas little support emerged for the hypothesis regarding religious values. The results are discussed in light of the various pathways through which religion may exhibit a protective influence.
Mexican Americans; religion; social capital; substance use; youths
This article examines key aspects of the school environment — its composition by ethnicity and acculturation — as important social contexts for understanding Mexican immigrant and Mexican American adolescents' drug use norms and behaviors. Results are presented based on surveys completed by Mexican-background students from 35 Phoenix. Arizona middle schools, whose enrollment ranged from a numerical minority to an overwhelming majority. Multivariate mixed models tested for the influence of school ethnic composition measures on substance use outcomes, while accounting for individual level predictors and for the nesting of data at the school level. The proportional representation of Latinos in the school was not a factor in an individual's drug use norms or drug use for the sample overall. Once students were broken down by acculturation status, however, ethnic composition had an effect. Less acculturated Mexican heritage students in schools with higher proportions of Latino students reported less substance use and less adherence to pro-drug norms. Further investigation using other measures of ethnic composition suggested that these effects were attributable to the larger presence of less acculturated Latinos in the school rather than more acculturated Latino students. These school-level effects support the individual-level results indicating that less acculturated Mexican American students face less daunting substance use risks. The results suggest that ethnic group size, but not necessarily numerical predominance, matters and that within-group differences influence the effect of a particular ethnic group's presence in the school. In other words, the majority does not always rule. These findings are interpreted using the concepts of segmented assimilation and school level social capital.
This study examined drug resistance strategies and substance use among adolescents from Monterrey, Mexico. The focus was strategies that U.S. adolescents use most often to resist using substances, including refuse (saying no), explain (declining with an explanation), avoid (staying away from situations where drugs are offered), and leave (exiting situations where drugs are offered). Using self-administered questionnaire data from a convenience sample of 327 Mexican students enrolled at two secondary schools (preparatorias), we tested whether frequent use of particular drug resistance strategies predicted actual substance use. Multiple regression results showed that different strategies were effective for different substances, that some effects were mediated by number of offers received, and that certain effects were stronger for females than for males. Students using the refuse strategy reported less cigarette use and less binge drinking; those using the avoid strategy reported less alcohol and cigarette use; and those using the leave strategy reported less binge drinking and, for females only, less marijuana use. Use of the explain strategy was not significantly related to substance use after controlling for use of other strategies. Findings are discussed in terms of Mexican cultural values and their implications for the design of prevention programs for Mexican youth.
Adolescents; Substance use; Substance use offers; Mexican youth; Drug resistance
Efforts to address youth substance use have focused on prevention among non-users and treatment among severe users with less attention given to youth occupying the middle ground who have used substances but not yet progressed to serious abuse or addiction. Using a sample from 35 middle schools of 1,364 youth who reported using substances, this study examined the effectiveness of a universal youth substance use prevention program, the SAMHSA Model Program keepin’ it REAL, in promoting reduced or recently discontinued alcohol, cigarette, and marijuana use. Discrete-time event history methods modeled the rates of reduced and recently discontinued use across four waves of data. Each substance (alcohol, cigarettes, and marijuana) was modeled separately. Beginning at the second wave, participants who reported use at wave 1 were considered at risk of reducing or discontinuing use. Since the data sampled students in schools, multi-level models accounted for the nesting of data at the school level. Results indicated that prevention program participation influenced the rates of reduced and recently discontinued use only for alcohol, controlling for baseline use severity, age, grades, socioeconomic status, ethnicity and gender. Among youth who reported use of alcohol in wave 1 (N= 1,028), the rate of reducing use for program participants was 72% higher than the rate for control students. The rate of discontinuing use was 66% higher than the rate for control students. Among youth who reported use of one or more of the three substances in wave 1 (N = 1,364), the rate of discontinuing all use was 61% higher for program participants than for control students. Limitations and implications of these findings and plans for further research are discussed.
Universal prevention; Substance use reduction; substance users; Adolescents
This study examines how neighborhood characteristics affect program efficacy. Data come from a randomized trial of a substance use prevention program called keepin’ it REAL, which was administered to a predominantly Mexican American sample of 4,622 middle school students in Phoenix, Arizona, beginning in 1998. Multilevel models and multiple imputation techniques address clustered data and attrition. Among less linguistically acculturated Latinos, living in poorer neighborhoods and those with many single-mother families decreased program effectiveness in combating alcohol use. High neighborhood immigrant composition increased program effectiveness. Unexpectedly, the program was also more effective in neighborhoods with higher rates of crime. There were no significant effects on program efficacy for the more linguistically acculturated Latinos and non-Hispanic White students. Findings are discussed in light of theories of neighborhood social disorganization, immigrant adaptation, and social isolation.
substance use; adolescents; neighborhoods; neighborhood effects; Latinos; Mexican Americans; acculturation; prevention; program efficacy; social control; social cohesion; social capital; treatment
This study explored relationships between several hypothesized dimensions of gender identity and substance use outcomes within a non-probability sample of adolescents in Monterrey, Mexico. Based on Mexican concepts of machismo and marianismo, four gender identity constructs were measured: aggressive masculinity, assertive masculinity, affective femininity and submissive femininity. The study assessed how well these gender identity measures predicted substance use behaviors, substance use intentions, expectancies, and normative approval, and exposure and vulnerability to substance offers. Data were drawn from questionnaires completed by 327 students from 2 Monterrey secondary schools. Multivariate ordered logistic and linear regression analyses, adjusted for school level effects, indicated that aggressive masculinity was associated with higher risk of drug use on most outcomes, while affective femininity was associated with lower risk on selected outcomes. Assertive masculinity was associated with only one of the outcomes examined and submissive femininity with none of them. Most gender identity effects persisted after controlling for biological sex, academic performance, age, and other gender identity measures. For two of the outcomes, the gender identity measures had significantly stronger effects for males than for females. The findings are interpreted in light of males’ higher risk for drug use and changes in gender roles and gendered behavior that are now occurring in Mexico as in the U.S.
Gender identity; Substance use; Gender gap; Adolescents; Youth; Mexico
Among a predominately Mexican and Mexican American sample of preadolescents, religiosity protected against lifetime alcohol, cigarette, and marijuana use and recent alcohol and cigarette use when religious affiliation was controlled. When religiosity was controlled, however, adolescents with no religious affiliation and adolescents who were religiously affiliated reported similar substance use outcomes. Interaction effects demonstrated that the protective effect of greater religiosity operated more strongly in some religions than in others for selected outcomes. Overall, the impact of religiosity on reported drug use did not differ significantly for more and less acculturated Latino youth.
adolescents; drug use; religiosity; Mexican American; acculturation
This study explored body image as measured by perceptions of weight and appearance and its impact on adolescent drug use among predominately Mexican American middle school students in the southwest. Outcomes analyzed included lifetime and recent alcohol, cigarette, and marijuana use and antidrug norms. Disliking one’s looks was more of a risk factor for boys, whereas negative weight perceptions were more of a risk factor for girls. Relative to more acculturated (English-dominant) Latinos (N=903), non-Latino Whites (N=121), and other non-Latino youth (N=107), less acculturated (Spanish-dominant) Latino youth (N=212) reported the poorest body image. However, more acculturated Latino youth with poor body image had the greatest risk of substance use. More acculturated Latino boys who disliked their looks reported relatively greater amounts of recent alcohol use, and those who rated their bodies as too thin reported higher lifetime cigarette use, a greater amount and frequency of recent cigarette use, and weaker antidrug norms. More acculturated Latina girls who thought they were too fat reported a greater amount and frequency of recent cigarette use. These findings suggest that low levels of acculturation may protect some Latino youth with poor body image from coping via substance use. In addition, they suggest that poor body image among some Latinos may result less from adoption of American thinness ideals but rather from attitudes and behaviors that devalue the characteristics of Latino appearance.
Body image; acculturation; substance abuse
This study examines neighborhood influences on alcohol, cigarette and marijuana use among a predominantly Latino middle school sample. Drawing on theories of immigrant adaptation and segmented assimilation, we test whether neighborhood immigrant, ethnic, and socioeconomic composition, violent crime, residential instability, and family structure have differential effects on substance use among youth from different ethnic and acculturation backgrounds. Data are drawn from self-reports from 3,721 7th grade students attending 35 Phoenix, Arizona middle schools. Analysis was restricted to the two largest ethnic groups, Latino students of Mexican heritage and non-Hispanic Whites. After adjusting for individual-level characteristics and school- level random effects, only one neighborhood effect was found for the sample overall, an undesirable impact of neighborhood residential instability on recent cigarette use. Sub-group analyses by individual ethnicity and acculturation showed more patterned neighborhood effects. Living in neighborhoods with high proportions of recent immigrants was protective against alcohol, cigarette, and marijuana use for Latino students at different acculturation levels, while living in predominantly Mexican heritage neighborhoods (mostly non-immigrants) was a risk factor for alcohol and marijuana use for less acculturated Latinos. There were scattered effects of neighborhood poverty and crime, which predicted more cigarette and alcohol use, respectively, but only among more acculturated Latinos. Inconsistent effects confined to bilingual and more acculturated Latinos were found for the neighborhood's proportion of single mother families and its residential instability. No neighborhood effects emerged for non-Hispanic White students. Results suggested that disadvantaged neighborhoods increase substance use among some ethnic minority youth, but immigrant enclaves appear to provide countervailing protections.
neighborhood effects; substance use; adolescents; Mexican Americans; acculturation
This research examined how family and individual factors influence three HIV/AIDS risk behaviors: having more than one sexual partner in the last three months, substance use at last sexual intercourse, and condom non-use at last sexual intercourse. The sample includes 89 sexually active American Indian adolescents living in a large Southwestern city. Logistic regression results revealed that family communication acts as a protective factor against HIV risk through a lower reported substance use during last sexual intercourse, but it did not appear to affect the number of multiple recent sex partners. Family and personal involvement in American Indian cultural activities, both low on average, had no effect on the outcomes. This study helps to fill the gap in knowledge on sexual health risk and protective factors among American Indian adolescents, an understudied group, and provides implications for intervention with American Indian youths and their families.
HIV/AIDS; family context; protective factors; American Indian youth
This article reports the results of a descriptive study conducted with middle school and high school age youth residing in northwestern Spain. The main outcome of the study is to advance knowledge about the drug use attitudes and behaviors of immigrants versus native youth in a social context where Latin American immigrants share a common language and a set of core cultural norms with the host society. The research was conducted by a bi-national Spain–US research team as a preliminary study leading to the development of joint culturally appropriate prevention interventions for youth in the northern region of Galicia, Spain. Surveys were administered in Spring 2005 to 817 students in 7th to 10th grades in 10 urban, secondary schools with high immigrant enrollment. The sample included Spanish natives (two-thirds) and Latin American immigrants (one-third), mainly from Colombia, Argentina, and Venezuela. Multiple regression analyses predicted substance use intentions, and a composite variable measuring lifetime and last 30-day frequency and amount of alcohol, cigarette and marijuana use. Controlling for the fact that the immigrant students were generally older and performing less well academically than natives, and for other predictors, Latin American immigrant youth were less at risk than native youth on their intentions to use substances and on their reported actual substance use. In a mediational analysis, most of the key explanatory variables in youth substance use etiology failed to account for the immigrant versus native differences, including a range of risk and protective factors for substance use, substance use norms, strength of ethnic identity, and degree of social integration within native-born social networks. Differential access to drugs mediated the immigrant–native gap in substance use intentions but did not mediate differences in actual substance use.
immigrants; youth; substance use; ethnic identity
Using a predominately Mexican-origin Latino sample of 5th grade students from the Southwestern United States, this study examined the relative effects of perceived discrimination and acculturation stress on substance use, and it assessed whether these effects were moderated by linguistic acculturation or time in the United States. Although rates of substance use were generally low in the sample, given the young age of the participants, over half (59%) of the sample perceived some discrimination, and almost half (47%) experienced some acculturation stress. Spanish-dominant and bilingual youth perceived more discrimination than English-dominant youth, whereas youth who have been in the United States five or fewer years perceived more discrimination than youth with more time in the United States. Youth who were Spanish-dominant or were recent arrivals experienced the most acculturation stress, with levels declining as linguistic acculturation and time in the United States increased. Multiple regression estimates indicated that perceived discrimination was associated with larger amounts and higher frequency of recent substance use and an array of substance use attitudes, such as stronger intentions to use substances, espousal of pro-drug norms, more positive substance use expectancies, and peer approval of substance use. Although acculturation stress was not associated with substance use, it was positively associated with several substance use attitudes, which are known antecedents of actual use. With a few exceptions, linguistic acculturation and time in the United States did not moderate the effects of perceived discrimination or acculturation stress.
This study examined how ethnic composition and linguistic acculturation within schools affected the efficacy of a youth substance use prevention model program. Data come from a randomized trial of the keepin' it REAL program, using a predominantly Mexican American sample of middle school students in Phoenix, Arizona. Schools were randomly assigned to a control group or to one of three culturally tailored intervention versions. We hypothesized that school ethnic and linguistic acculturation composition (percent Latino, percent non-English speaking at home) and individual level of linguistic acculturation jointly would moderate the efficacy of the prevention program, as indicated by students' alcohol, marijuana, and cigarette use. Using multilevel linear modeling and multiple imputation techniques to manage clustered data and attrition, results showed that desired program effects varied by the linguistic acculturation level of the school, the program version, and individual acculturation level. The Latino intervention version was more efficacious in schools with larger percentages of non-English speaking families, but only among less linguistically acculturated Latino students. There were no significant school level program effects connected to the percentage of Latino students at school, the other versions of the program, or among more linguistically acculturated students.
The prevention literature has given little attention to how parental influences affect substance use among Mexican origin adolescents, even though they form part of the largest ethnic minority group in the United States. This study explored the effects of three types of parental influences—parental monitoring of the child's whereabouts, degree of parental permissiveness, and the strength of parental injunctive norms discouraging substance use—on alcohol, cigarette, and marijuana use and anti-drug norms. Results showed that parental permissiveness and parental injunctive norms, particularly anti-drug injunctive norms, had the strongest effects on the substance use outcomes, but parental monitoring generally was not a significant predictor. These results and implications for prevention are discussed in light of Mexican cultural norms toward substance use, gender roles, and family roles.
This article describes the development and immediate effects of a small-group intervention designed to complement a school-based prevention program for children and youth. The REAL Groups intervention is the result of a partnership with predominately Mexican American schools located in the central city neighborhoods of a southwestern U.S. metropolitan area. The group members (N = 115) were fifth graders from six central city schools. Group members were identified and referred by their teachers as in need of additional support beyond the keepin'it REAL classroom-based substance abuse prevention intervention, or they were invited by the referred students. The REAL Groups followed a mutual aid approach, and Masters in Social Work student interns trained in the REAL Groups intervention served as the group facilitators. This article describes the small-group intervention and provides an initial report on the results by comparing the small-group members (n = 115) with Mexican-heritage classmates (n = 306) who only received the classroom-based keepin' it REAL prevention intervention. This is a feasibility study in preparation for the follow-up study with seventh graders. As expected due to the low drug-use rates reported by fifth-grade participants, the effectiveness results were inconclusive. The immediate findings, however, provide important information about the design and evaluation of culturally specific group interventions with acculturating children. The article provides important methodological and practice implications for small-group school-based interventions as well as recommendations for future research.
mutual aid; small groups; substance use; prevention; at risk; youth; children
This study tested for gender differences in the impact of linguistic acculturation on pro-drug norms, substance use intentions, and actual substance use among youth of Mexican heritage in a large metropolitan area in the Southwest United States. The authors analyzed baseline survey data provided by 2,487 middle school students of Mexican heritage who were part of a larger, multiethnic randomized efficacy trial of a drug abuse prevention program. Using multi-group structural equation modeling, the authors found that linguistic acculturation was positively and directly related to adherence to pro-drug norms, substance use intentions, and recent alcohol use, controlling for age, poor grades, and socioeconomic status. In addition, linguistic acculturation had an indirect effect on substance use intentions and recent alcohol use through pro-drug norms. The direct effect of linguistic acculturation on pro-drug norms was stronger for girls than for boys, as was its indirect effect on substance use intentions.
acculturation; gender differences; Mexican American youth; substance use; substance use norms
This community-based exploratory study examined the effects of a history of violence, ethnic identification, and acculturation status on HIV risk among a majority Latino sample of youth living in a large metropolitan area of the Southwest in the United States. The participants reported high rates of violence and attitudes that put them at risk for HIV/AIDS infection. They participated in 1 of 2 prevention interventions offered by a local non-governmental organization. The first intervention was tailored for adjudicated youth (N=49) who were either institutionalized or were returning to the community after involvement with the criminal justice system. The second intervention targeted youth (N=32) who were homeless/runaway and/or self-identified as gay, lesbian, bisexual, or transgender (GLBT). T-tests and linear regression were used to determine the differences between youth reporting a history of violence by type of perpetrator, its relationship with HIV risk, and the role of ethnic identification and acculturation status as potential protective factors. Violence by a family member was the most common type of violence reported, with a history of violence positively related to HIV risk. Ethnic identification and linguistic acculturation had a protective effect against HIV risk among the homeless and GLBT youth but not among the adjudicated youth.
HIV/AIDS; adjudicated youth; homeless/runaway; GLBT; youth; violence
This study aims to comparatively examine drug use in Arizona and Spain, in order to know if similarities and differences in drug use patterns justify the administration in Spain of U.S. prevention intervention programs. Data were obtained from independent samples of seventh-grade students recruited from urban public schools and surveyed in 1998: 4,035 ethnically diverse Arizona students (Latinos and non-Hispanic Whites), and 2,243 Spanish-White students. Comparisons using Odds ratios and Chi-square tests allowed assessment of differences in drug use rates between preadolescents in Arizona and Spain taking into account gender. Furthermore, ethnicity differences in preadolescent drug use and in psychosocial risk factors were explored using multivariate analysis (ANOVA and logistic regression). Our results showed similar trends in drug use between Arizona and Spain students, with gateway drugs already in use by early adolescents, and with higher rates of drug use among males than among females. However, cross-national differences in marijuana/cannabis use were noteworthy: Arizona preadolescents were over 25 times more likely to report marijuana/cannabis use than preadolescents from Spain. Moreover, when ethnic differences were considered, Latinos in Arizona reported higher marijuana/cannabis use compared with non-Latino students. Drug use patterns among Latino preadolescents, as well as the relevance of some risk factors among the diverse groups, were strongly influenced by their level of acculturation. Study limitations and the implications of our findings for early drug use prevention and future research are discussed.
Preadolescents; substance use; cross-national; Spain; Arizona; gender; ethnicity
This study explores the extent to which parental and peer behaviors and norms may affect substance use, personal anti-drug norms and intentions to use drugs in a group of Mexican heritage preadolescents in the Southwest, and whether these parental and peer influences differ according to gender. Secondary data from a randomized trial of a drug prevention program was used. The sample consisted of 2,733 adolescents. The outcomes were recent alcohol, cigarette, and marijuana use, personal anti-drug norms and intentions to use drugs. In this study, peer variables were more consistently related to the outcomes than parent variables, with the exception of parental injunctive norms which were the most predictive parent factor. Recommendations are provided to further study the protective processes that are maintained through the transition into adolescence and acculturation as a foundation for the design of resiliency-focused prevention interventions.
parental monitoring; parental permissiveness; injunctive norms; personal anti-drug norms; substance use; peers; Mexican adolescents