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Is it getting better? An analytical method to test trends in health disparities, with tobacco use among… Homma, Yuko; Saewyc, Elizabeth; Zumbo, Bruno D May 23, 2016

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RESEARCH Open AccessIs it getting better? An analytical method totest trends in health disparities, withtobacco use among sexual minority vs.heterosexual youth as an exampleYuko Homma1, Elizabeth Saewyc2* and Bruno D. Zumbo3AbstractBackground: Previous studies have documented higher health risks for lesbian, gay, and bisexual youth comparedto heterosexual youth. However, none has reported whether the sexual orientation-based gaps have widened,narrowed, or remained unchanged over time. The purpose of this study was to develop a way to test differencesin trends between sexual minority and heterosexual youth cohorts in population-based studies, with cigarettesmoking as an exemplar.Methods: We analysed the Minnesota Student Survey of 1998–2010, a repeated, cross-sectional census ofadolescent health in grades 9 and 12. Our sample was students with recent sexual experience (Ns = 17,376–19,617).Sexual orientation was measured by gender of sexual partners in the past 12 months: students with onlyopposite-gender partner(s) (OPPOS), students with both male and female partners (BOTH), students with onlysame-gender partner(s) (SAME). We used logistic regressions to examine trends in prevalence of past-monthcigarette smoking from 1998 to 2010, separately for each orientation group. We then applied novel interactionanalyses to test whether disparities in smoking prevalence between OPPOS and SAME/BOTH changed over time.Results: Recent smoking rates decreased over time among all orientation groups. BOTH adolescents were morelikely than OPPOS adolescents to report past 30-day smoking, but there were no significant differences betweenSAME adolescents and OPPOS adolescents. Year-by-orientation interactions indicated the gap between BOTHadolescents and OPPOS adolescents widened from 1998 to 2004, then persisted between 2004 and 2010. Nosignificant interaction effects were observed between SAME adolescents and OPPOS adolescents.Conclusions: All orientation groups had decreasing trends in recent cigarette smoking; however, disparities insmoking rates remain between heterosexual adolescents and bisexual adolescents. These results provide a newmethod of not just documenting trends within minority groups, but examining whether health equity is improvingfor them compared to dominant groups.Keywords: Sexual orientation, Adolescents, School surveys, Tobacco use, Cohort trends, Interaction analysis,Health disparities* Correspondence: elizabeth.saewyc@ubc.ca2Stigma and Resilience Among Vulnerable Youth Centre, University of BritishColumbia School of Nursing, T201-2211 Wesbrook Mall, Vancouver, BC V6T2B5, CanadaFull list of author information is available at the end of the article© 2016 The Author(s). Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, andreproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link tothe Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.Homma et al. International Journal for Equity in Health  (2016) 15:79 DOI 10.1186/s12939-016-0371-3BackgroundA substantial body of population-based evidence inNorth America, Europe, and elsewhere has documentedsignificant health disparities for lesbian, gay, and bisex-ual youth (sexual minority or LGB youth) compared totheir heterosexual peers [1]. They experience dispro-portionately higher rates of discrimination and violenceexposure [2]; higher prevalence of alcohol and otherdrug use [3–5]; equal or higher rates of sexual healthbehaviours, including adolescent pregnancy involve-ment [6, 7] and for some, greater risk of sexually trans-mitted infections such as HIV [8, 9]; and higher rates ofdepression and suicide attempts [10]. Sexual minorityyouth have also been more likely to report tobacco usethan their peers in studies in the USA [4, 11], in theUK [12] and in Canada [13, 14].Much of the research examining these health dispar-ities links them to stress as a result of stigma, discrim-ination, and violence targeted toward sexual minoritypeoples [1]. Yet the past decade has seen sweeping im-provements in the social and legal status of sexual mi-nority populations in a number of countries, includingchanges in human rights law [15] and in legalizationof same-sex marriage [16]. There have even been safeschool policies enacted to reduce homophobic harass-ment and bullying among youth in schools [17]. Thisraises the question: is it getting better? Are thesehealth risks beginning to improve among LGB youth?There are a limited number of regularly repeatingpopulation-based adolescent health surveys that in-clude measures of sexual orientation, and have beenrepeated over a long enough time period to begin todocument trends in health and risk behaviours [6, 18].Declines in health-compromising behaviours or im-provements in health outcomes among sexual minoritygroups, while good news in themselves, cannot tell uswhether the disparities between them and heterosexualyouth are also improving. For example, tobacco usehas been declining among adolescents and adultsthroughout North America and much of Europe overthe past decade [19], so if there are declines in tobaccouse among LGB youth, they may be matched by simi-lar declines among heterosexual youth, and thus thegap between them remains. Alternately, tobacco usemay be declining at a slower rate for sexual minorityyouth, widening the gap between them and hetero-sexual youth, or at a faster rate, narrowing the gap inhealth equity. Our search of the literature turned upno studies that examine trends over time in healthequity between heterosexual and sexual minoritypeople, whether adults or adolescents. Indeed, insearching the literature, we found no articles that dir-ectly tested trends in health gaps between any groups,on any health issue.Part of the reason for this lack of research may be alack of appropriate analytical methods. Much of thetime, health disparities are documented using logistic re-gressions in order to calculate odds ratios or risk ratiosbetween the dominant majority and the marginalizedsubgroup. Repeating those analyses separately withinmultiple cohorts over time and displaying the odds ra-tios in a table, or graphing them in a figure, which hasbeen used in the past to show persistent disparities [6],is insufficient to accurately evaluate trends in disparities.This is because odds ratios should not be directly com-pared, not even with confidence intervals, due to under-lying heterogeneity that cannot be accounted for inlogistic regression models [20]. However, in the past dec-ade, some studies have developed methods to compareodds ratios between independent samples for other pur-poses, using interaction terms. For example, Altman andBland [21] recommended using interactions in logisticregression to help determine whether treatment effectsdiffer between two subgroups in intervention studies.These interaction terms produce a ratio of odds ratioswithin the logistic model. Our question is, could thesemethods be adapted to test year by orientation group in-teractions instead, with heterosexual youth as the refer-ent group for orientation, to determine whether the gapis narrowing, widening, or unchanged? If so, this wouldoffer a new method for examining health equity trendsamong marginalized groups.Thus, our primary purpose was to adapt these ap-proaches, in order to test trends in health disparities overtime between sexual minority and heterosexual youth co-horts in population-based studies. In this analysis, weused disparities in tobacco use among students in thestate of Minnesota in the United States of America asthe exemplar case to demonstrate the method.MethodsDataData were from the Minnesota Student Survey (MSS), across-sectional statewide anonymous census of adoles-cent health administered every 3 years to public schoolstudents in grades 9 and 12 in Minnesota. All school dis-tricts were invited to participate and school district par-ticipation rates were approximately 90 %. Approximately75,000 students in grades 9 and 12 participated in eachyear of the survey. The detailed survey procedure hasbeen described elsewhere [22]. We used a weighted,merged data set from 1998 to 2010 for trend analyses,including only school districts that participated in allsurvey years from 1998 to 2010. The University of Brit-ish Columbia Behavioural Research Ethics Board ap-proved the study under which these specific analyseswere conducted (certificate # H12-00477).Homma et al. International Journal for Equity in Health  (2016) 15:79 Page 2 of 8SampleAs a secondary analysis, we were limited in the meas-ure of sexual orientation to a consistent measure acrossall the years: our sample only included students whoprovided responses to two questions: “During the last12 months, with how many different male partnershave you had sexual intercourse?” and “During the last12 months, with how many different female partnershave you had sexual intercourse?” and to gender. Thusour sample consisted of recently sexually active stu-dents, grouped by gender of sexual partner into threecategories: those who had sex with opposite-genderpartner(s) only (OPPOS), those who had sex withsame-gender sexual partner(s) only (SAME), and thosewho had sex with both male and female partners(BOTH). Approximately 30 % of students from the ori-ginal surveys in each year reported having had sexualintercourse with male and/or female partners in the last12 months (Ns = 17,376–19,617).Data were weighted to adjust for differences in studentparticipation rates among school districts in a given year[22]. The weighted sample size is summarized in Table 1,with the percent of grade 12 students noted for eachorientation and gender group (the percent of grade 9students is the inverse of that percent, as only twogrades are surveyed).MeasuresSmoking in the last 30 days was assessed with the item,“During the last 30 days, how frequently have you smokedcigarettes?” Having never smoked a cigarette in the last30 days was coded as “No” and having smoked less thanone cigarette per day or more frequently in the last30 days as “Yes”.AnalysesThere were significant gender differences in the preva-lence of tobacco use, as well as the prevalence of same-gender or both-gender sexual behaviours (data notshown), so all analyses were stratified by gender.In order to examine trends over time within each ofthree orientation groups, we first described the preva-lence of cigarette smoking in each of 5 years, separatelyby sexual orientation. Chi-square test for trend was usedto compare 1998, 2004, and 2010 data. Because grade 9respondents may have completed a subsequent surveywhen they were in 12th grade, we selected only those 3years, to ensure sample independence. Likewise, giventhat there may have been changes over time in the ageat which adolescents initiate sexual behaviour or tobaccouse, we also conducted logistic regressions, adjusted forgrade, to assess changes in the prevalence of cigarettesmoking from 1998 to 2004 and from 2004 to 2010within each orientation group. An odds ratio (OR)greater than 1 indicates an increasing trend, and an ORless than 1 indicates a decreasing trend.Next, to examine sexual orientation-based disparitiesin tobacco use within each of the five survey years, weconducted grade-adjusted logistic regressions. TheOPPOS group was used as a reference category. Thus,an OR of > 1 indicates that SAME or BOTH studentswere more likely than OPPOS students to report havingsmoked a cigarette in the last 30 days. An OR of < 1 in-dicates a lower likelihood of recent smoking amongSAME or BOTH than among OPPOS.Finally, we examined whether differences in smokingprevalence between OPPOS and SAME and betweenOPPOS and BOTH widened, narrowed, or stayed thesame from 1998 to 2004 and from 2004 to 2010. To dothis, we computed interaction terms of sexual orienta-tion and survey year in a logistic regression model thatincluded sexual orientation, survey year, orientation-by-year interaction, and grade, with OPPOS as the referencegroup for orientation. In this analysis, a statistically sig-nificant interaction term suggests that the gap in recentsmoking rates between OPPOS and SAME or BOTHhas significantly widened or narrowed over time. Basi-cally, this interaction term indicates a ratio of ORs, i.e., aratio of the OR of smoking by orientation group for agiven year (i.e., 1998 or 2010) to the odds of smokingamong SAME or BOTH students vs OPPOS studentsfor a reference year (i.e., 2004). An interaction OR wasgreater than 1 when the OR for a given year was greaterthan that of the reference year, whereas an interactionTable 1 Samples Students By Gender of Sexual Partners in theMinnesota Student Surveys1998 2001 2004 2007 2010MaleOPPOS 7,999 7,347 7,412 7,659 7,832(Grade 12, %) (58.7 %) (63.1 %) (63.4 %) (64.9 %) (66.0 %)BOTH 1,176 1,008 1,010 1,744 1,632(Grade 12, %) (40.6 %) (46.2 %) (46.2 %) (57.7 %) (55.3 %)SAME 148 142 172 250 268(Grade 12, %) (51.4 %) (49.3 %) (48.3 %) (54.4 %) (60.4 %)FemaleOPPOS 8,721 8,210 8,386 8,762 8,869(Grade 12, %) (66.8 %) (69.9 %) (69.1 %) (70.7 %) (71.3 %)BOTH 367 515 575 658 765(Grade 12, %) (47.4 %) (45.6 %) (39.8 %) (48.8 %) (50.6 %)SAME 45 56 82 112 138(Grade 12, %) (48.9 %) (44.6 %) (39.0 %) (41.1 %) (58.0 %)Note. Data were weightedOPPOS Students who had sex with partner(s) of the opposite gender only,BOTH Students who had sex with both male and female partners, SAMEStudents who had sex with partner(s) of the same gender onlyHomma et al. International Journal for Equity in Health  (2016) 15:79 Page 3 of 8OR was smaller than 1 when the OR for a year wassmaller than the OR of the reference year. To interpretthese interaction ratios of ratios, however, it is importantto pay attention to the main effect OR in the model aswell: when both the OR for a given year and OR for areference year are greater than 1, an interaction ORgreater than 1 suggests the sexual orientation-based dis-parity in a year was larger than in the reference year (i.e.,the gap is widening), and an interaction OR less than 1suggests the orientation-based difference in a year wassmaller than in a reference year (i.e., the gap is narrow-ing). In contrast, when both the original year ORs aresmaller than 1, an interaction OR greater than 1 suggeststhe inverse: that the orientation-based difference in agiven year is smaller than in a reference year (gap is nar-rowing), whereas an interaction OR less than 1 suggeststhe orientation-based difference in a given year is greaterthan in the reference year (the gap is widening). To de-termine whether the gap has widened or narrowed, oneneeds to refer to the OR for the sexual orientation-baseddifference in a given year and in a reference year alongwith the interaction OR. See Table 2 for a summary ofinterpreting odds ratios for the interaction terms.A question may arise, why are these complex inter-action terms needed for testing trends in disparities?Couldn’t we just compare the trends in the prevalence(i.e., the percents) between heterosexual and sexual mi-nority youth, rather than comparing trends in the oddsratios or adjusted odds ratios? Indeed, Asada [23] notesthe importance of examining absolute measures of in-equalities that take into account the starting point, orthe absolute level of the health issue in each group,when comparing populations. Asada asserts that by cal-culating the absolute change in each group by subtract-ing the last year percent from first year percent, theabsolute size of the change can hint at the trend in theinequality, i.e., the inequality is greater when the domi-nant group improves more than the minority group, andit is smaller when the minority group improves morethan the minority group. The problem with directlycomparing trends in prevalence between heterosexualand sexual minority youth as an absolute difference inpercentage points is that these results may be somewhatmisleading, because simple percents do not account forage differences in the two samples that can provide acompeting explanation for the disparities. Because sexualorientation is a developmental task of adolescence, anddevelopment itself has a wide range of normal variationin timing, not all young people go through puberty, de-velop attractions, or begin romantic or sexual relation-ships at the same age, and if the attractions or identityare stigmatized, it tends to be longer before youngpeople publicly disclose that, even if they act on theknowledge earlier [1]. Thus, in secondary school popu-lation surveys throughout the world, researchers havegenerally noted significant age differences between het-erosexual and sexual minority youth, no matter howsexual orientation is measured [1, 24, 25], althoughthose age differences are not always in the same direc-tion. For example, youth engaging in same-gender orboth-gender sexual behaviour tend to report that atslightly younger ages than those engaging in opposite-sex sexual behaviours [6], which appears to be due inpart to their greater risk for being targeted for sexualabuse during early adolescence [2, 8].In contrast, among those with same-sex attractions,stigma may delay their recognition of and public disclos-ure of such attractions [1]. And when it comes to iden-tity labels, because of our heteronormative society, manyadolescents who have not yet developed attractions orengaged in sexual behaviour identify as the default het-erosexual, and it is only later during adolescence thatthey identify as lesbian, gay, or bisexual [26]. Thus, inpopulation-based surveys, the average age of sexual mi-nority youth tends to be different from the average ageamong heterosexual youth, but may be older or younger,depending on whether the sample is limited to sexuallyexperienced youth, or all youth. And since smoking itselfhas a maturational trend (older youth are more likely tosmoke than younger adolescents), unless the analysescontrols for age (or grade in studies where the sample isonly within discrete grades), the prevalences for hetero-sexual and sexual minority youth are not truly compar-able, they're confounded by demographic differences inage. Therefore, age- or grade- adjusted regressions arepotentially more appropriate comparisons to use inorder to identify trends in disparities.Documenting the strength of disparities betweengroups, and testing trends in disparities, however, areonly part of the information needed to understand andaddress health equity issues. Odds ratios, even adjustedodds, are a measure of the relative strength of the dis-parity between two groups, but provide no informationabout the scope or magnitude of the problem. For ex-ample, an odds ratio of 2.0 could describe a disparity intobacco use between two groups when the difference isTable 2 Interpretation of Odds Ratios for Analyses of Trends inDisparitiesOriginalORsaORs forinteraction termsSexual orientation-based disparitiesYear 1998 or 2010 >1 >1 WideningYear 2004 (reference) <1 NarrowingYear 1998 or 2010 <1 >1 NarrowingYear 2004 (reference) <1 WideningNote. OR Odds ratioaORs from logistic regression models that examine sexual orientation-baseddisparities in tobacco use within each of the 3 years (1998, 2004, and 2010)Homma et al. International Journal for Equity in Health  (2016) 15:79 Page 4 of 81.5 % vs. 3.0 %, or when it is 45 % vs. 90 %, but mostpeople would find the second disparity far more urgenta concern. As well, the size of the percentage changewithin a group over time may provide a clue as to whichgroup’s improvement or decline might be driving thewidening or narrowing (or unchanged) gap between thegroups. Therefore, it is important to report the preva-lence to give readers a sense of the size of the issue,while using age-adjusted regressions to describe thestrength of the disparity between both groups as an ad-justed odds ratio, and to test the trends in the disparityusing the ratio of adjusted odds ratios.Results and discussionTrends in past-month cigarette smoking within eachorientation groupAs shown in Table 3, recent cigarette smoking rateshave generally declined over time within all sexualorientation groups. Past 30-day smoking rates have de-creased from 1998 to 2004 among all male groups, butin 2010, smoking in the last 30 days prevalence de-creased compared to 2004 among OPPOS boys andBOTH boys, but not among SAME boys. Among girls,significant declines from 1998 to 2004 were observedamong OPPOS and BOTH but not among SAME, how-ever, all female groups in 2010 were less likely thantheir 2004 counterparts to report smoking cigarettes inthe last 30 days. The absolute differences in decliningprevalence among the OPPOS boys (26.8 points) andgirls (34.4 points) appears to be larger than it is amongBOTH and SAME students (24.4 for BOTH and 21.1for SAME boys; 25.8 for BOTH and 21.5 for SAMEgirls), however, it is important to remember these arenot adjusted for age.Disparities in smoking between sexual minority andheterosexual groups in each yearTable 4 presents odds ratios (ORs) adjusted for grade todocument disparities in recent cigarette smoking be-tween sexual minority and heterosexual students withineach survey year. BOTH and SAME groups were com-pared to the reference group of OPPOS. Overall, Asshown in Table 3, BOTH boys and BOTH girls weremore likely than their OPPOS peers to report havingsmoked a cigarette in the last 30 days. On the otherhand, there were no significant differences in recentsmoking between SAME groups and OPPOS groups, ex-cept for boys in 2001, when SAME boys were signifi-cantly less likely than OPPOS boys to have smoked acigarette in the last 30 days. There were no grade-adjusted significant differences between SAME girls andOPPOS girls in recent tobacco use in any year.Trends in sexual orientation disparities in smoking: Is itgetting better?All sexual orientation groups had declining trends in last30-day cigarette smoking between 1998 and 2010. How-ever, BOTH boys and girls continued reporting higheradjusted odds of smoking than their OPPOS peers. Wethen examined whether the differences in smoking ratesby sexual orientation have been smaller or larger from1998 to 2004 and from 2004 to 2010. ORs for inter-action terms of survey year and sexual orientation arepresented in Table 5. The statistically significant inter-action between BOTH and year 1998 for last 30-daysmoking among boys and girls indicates that the gap be-tween BOTH and OPPOS has widened from 1998 to2004, then persisted between 2004 and 2010. The oddsratios were from 1.36 to 1.73 among BOTH boys andfrom 1.66 to 2.36 among BOTH girls (Table 3). ThereTable 3 Trends in Prevalence of Recent Cigarette Smoking Across Years, within Sexual Orientation GroupsEver smoked cigarettes in the last 30 days (%) Trend 1998 – 2004b Trend 2004 – 2010c1998 2001 2004 2007 2010 p-valuea ORd (95% CI) ORd (95% CI)MaleOPPOS 56.3 47.0 38.5 34.1 29.5 < .001 0.48 (0.45, 0.51) 0.66 (0.62, 0.71)BOTH 63.3 54.6 50.9 40.1 38.9 < .001 0.59 (0.49, 0.70) 0.59 (0.50, 0.70)SAME 52.1 35.0 34.5 35.7 31.0 < .001 0.48 (0.30, 0.76) 0.83 (0.54, 1.25)FemaleOPPOS 63.9 52.9 44.6 36.3 29.5 < .001 0.46 (0.43, 0.48) 0.52 (0.49, 0.56)BOTH 75.8 67.3 66.7 56.9 50.0 < .001 0.63 (0.46, 0.85) 0.51 (0.40, 0.64)SAME 55.8 40.0 48.1 31.7 34.3 .006 0.74 (0.35, 1.59) 0.53 (0.30, 0.96)Note. Data were weighted. OR in bold indicates p < .05aChi-square test for trendbReference year = 1998cReference year = 2004dAdjusted for gradeOPPOS Students who had sex with partner(s) of the opposite gender only, BOTH Students who had sex with both male and female partners, SAME Students whohad sex with partner(s) of the same gender only, OR Odds ratio, CI Confidence intervalHomma et al. International Journal for Equity in Health  (2016) 15:79 Page 5 of 8were no significant interaction effects among SAMEgroups compared to OPPOS groups, and no dispar-ities in tobacco use. The widening gap between BOTHand OPPOS groups may be due to steeper declines intobacco use among OPPOS groups than amongBOTH groups.In this paper, we have documented trends in recentcigarette use among sexually active heterosexual andsexual minority adolescents in Minnesota schools be-tween 1998 and 2010. As demonstrated in recent studiesof tobacco use among general populations of adolescentsin high-income countries, we found steady declines intobacco use within each orientation group across theyears. In each year of the survey, we found disparities inpast-month cigarette smoking between youth with bisex-ual vs. heterosexual sexual behaviours, which are similarto findings from other cross-sectional studies. In con-trast to other studies, however, we did not find dispar-ities between youth who report only same-gender sexualbehaviour and those with heterosexual behaviour. Thismay be partly explained by differences in how sexualorientation is measured in the Minnesota StudentSurvey as compared to other studies, as some studiescombine lesbian, gay and bisexual adolescents, thuspotentially masking differences within sexual minoritygroups. Likewise, studies that use attraction or identityas the sexual orientation measure, although generallyconsidered a more valid measure than behaviour alone[1, 26], may end up combining youth with solely same-gender sexual partners and those with both-gendersexual partners, because attraction, identity and actualsexual behaviour are not necessarily concordantamong adolescents [9, 24, 25]. However, other studieshave documented higher levels of health challengesamong bisexual youth and adults, in part because oflack of acceptance in gay and lesbian communities aswell as heterosexual communities, and these dispar-ities in tobacco use for youth with bisexual behaviourare of concern.We also demonstrated a novel technique for testingwhether these disparities between sexual minority andheterosexual youth tobacco use were significantly in-creasing, declining, or unchanged, and found that thegap between bisexual and heterosexual youth’s tobaccouse widened between 1998 and 2004 for both boys andgirls reporting both-gender sexual partners, and thesedisparities continued between 2004 and 2010. This ana-lysis suggests that while population-wide interventionsto reduce tobacco initiation among adolescents is havingsome effect on sexual minority youth, among those withbisexual behaviour, the interventions are not as effectiveas on those with exclusively monosexual behaviour,whether opposite-sex only or same-sex only. The rea-sons for such widening disparities over the past decadeare not clear, but one possible explanation is that bisex-ual invisibility, or biphobia in both mainstream commu-nity and LGBTQ communities increase the minoritystress for bisexual adolescents, and reduce their socialsupports. Thus, additional targeted interventions may beneeded, either to reduce biphobia and stigma-relatedTable 4 Sexual Orientation Disparities in Recent Cigarette Smoking, within Year: Odds Ratiosa and 95 % Confidence Intervals1998 2001 2004 2007 2010MaleOPPOS ref ref ref ref refBOTH 1.36 (1.19, 1.55) 1.43 (1.25, 1.64) 1.73 (1.51, 1.99) 1.33 (1.19, 1.48) 1.60 (1.43, 1.80)SAME 0.86 (0.62, 1.19) 0.63 (0.44, 0.90) 0.87 (0.63, 1.20) 1.12 (0.86, 1.47) 1.10 (0.84, 1.44)FemaleOPPOS ref ref ref ref refBOTH 1.66 (1.30, 2.13) 1.76 (1.45, 2.14) 2.36 (1.96, 2.84) 2.27 (1.92, 2.68) 2.33 (2.00, 2.71)SAME 0.67 (0.36, 1.24) 0.56 (0.33, 0.97) 1.08 (0.69, 1.70) 0.79 (0.52, 1.20) 1.24 (0.87, 1.78)Note. Data were weighted. 95 % confidence intervals are in parentheses, Odds ratios in bold indicate p < .05aAdjusted for gradeOPPOS Students who had sex in past year with partner(s) of the opposite gender only, BOTH Students who had sex in past year with both male and femalepartners, SAME Students who had sex in past year with partner(s) of the same gender only, ref Reference groupTable 5 Trends in Disparities in Recent Cigarette Smoking:Interactions Between Sexual Orientation and YearMale FemaleORa (95% CI) ORa (95% CI)OPPOS by Year 2004 ref refBOTH by Year 1998 0.81 (0.67, 0.98) 0.73 (0.54, 0.99)BOTH by Year 2010 0.91 (0.76, 1.08) 0.98 (0.77, 1.24)SAME by Year 1998 1.00 (0.63, 1.58) 0.65 (0.30, 1.38)SAME by Year 2010 1.25 (0.82, 1.91) 1.15 (0.65, 2.04)Note. Data were weighted. Odd ratio in bold indicates p < .05aThe model included sexual orientation, survey year, and grade along withorientation-by-year interactionsOR Odds ratio, CI Confidence interval, OPPOS Students who had sex withpartner(s) of the opposite gender only, BOTH Students who had sex with bothmale and female partners, SAME Students who had sex with partner(s) of thesame gender only, ref Reference groupHomma et al. International Journal for Equity in Health  (2016) 15:79 Page 6 of 8stress or improve social supports, in order to furtherreduce the prevalence of tobacco use among bisexualadolescents.Strengths and limitationsAs with all studies, this analysis has both strengths andlimitations. A key strength is the use of regularly re-peated large-scale population surveys of adolescents inschool, with one of the few such surveys that coversmore than a decade and includes a measure of sexualorientation, with large enough sample sizes to disaggre-gate those with same-gender only and both-gender sex-ual partners. As well, the use of an established statisticaltechnique, although applying it for a novel analyticalpurpose, is a clear innovation that may be useful formeasuring trends in health equity for sexual minorityyouth and potentially other marginalized groups.At the same time, it must be acknowledged that themeasure of sexual orientation itself is sub-optimal. Sincethe majority of adolescents in North America are notsexually active, a measure of sexual orientation that re-lies on sexual behaviours will inevitably exclude a signifi-cant proportion of the population, either heterosexual orsexual minority youth. Sexual orientation has been moreaccurately assessed among adolescents as attractions oridentity labels [26] as there is noted discordance be-tween attractions/identity and actual sexual behaviour[9, 24, 25]. As well, focusing on the gender of past yearsexual partners may misclassify youth with only onesexual partner in the past year, whether same-gender orother-gender; if any previous partners in earlier yearswere of a different gender, they would more accuratelybelong in the both-gender category. These trend ana-lyses should be replicated with other population-basedsurveys that also assess sexual orientation through at-traction or identity measures, so that youth who are notsexually experienced are included in the study. Theseresults are from a single state in the US, Minnesota; dif-ferent environments, laws, culture and history in otherregions of the US might influence trends in health dis-parities for sexual minority youth in different directionsthan we found in Minnesota. Similarly, trends in dispar-ities may look different in Canada, or in other countriesoutside of North America; these methods should beused where possible to document whether disparitiesare getting better in different regions globally, whereverit is feasible given existing population surveys. Finally,as a study of youth in school, the results cannot be gen-eralized to youth who are not attending school.ConclusionsThis is among the first few studies to document trendsin health and risk behaviours among sexual minority ad-olescents, and to our knowledge, is the first to actuallytest trends in health disparities for them. The resultsshow the importance of not only documenting trendsamong sexual minority populations, but also document-ing whether health equity is improving for them com-pared to dominant groups. This information can helpguide policies, practices, and resource allocation to re-duce health inequities.This innovative method of testing trends in health dis-parities, however, to see if the gap is narrowing, widen-ing, or unchanged, has relevance for health equitybeyond that of sexual minority people. The techniquecould be applied within national, regional, and localpopulation studies to evaluate trends in health disparitiesamong other groups who experience significantly higherhealth risks or poorer health outcomes as a result of so-cial marginalization; for example, disparities betweenethnocultural minority groups and the dominant groupsin societies, or between low-income groups and thosewith higher socio-economic status. It may not be enoughto track changes in health outcomes for Indigenous pop-ulations, or for groups of children in foster care, for ex-ample, without placing these trends in the context of thewider community’s trends in health improvements. Thisnew approach to testing the trend in disparities is oneway to take context into account, and will provide im-portant information to guide health equity initiatives formarginalized groups.AbbreviationsBOTH, adolescents who had sex with both male and female partners; LGB,lesbian, gay, and bisexual; OPPOS, adolescents who had sex with opposite-gender partner(s) only; SAME, adolescents who had sex with same-genderpartner(s) only.AcknowledgmentsThis study was funded by grants #CPP 86374 and #MOP 119472 from theCanadian Institutes of Health Research (Saewyc, PI). The authors acknowledgethe Minnesota Departments of Health, Human Services, and Education forpermission to access the Minnesota Student Surveys.Authors’ contributionsYH, ES, and BDZ conceptualized and designed the study. YH analyzed thedata, interpreted the results, and drafted much of the manuscript. ES securedaccess to the Minnesota Student Survey data, contributed to interpreting theresults, wrote portions of the manuscript, and revised the final manuscript.BDZ guided data analysis, interpreted the results, and edited the finalmanuscript. All authors read and approved the final manuscript.Competing interestsThe authors declare that they have no competing interests.Author details1Mukogawa Women’s University School of Nursing, Hyogo, Japan. 2Stigmaand Resilience Among Vulnerable Youth Centre, University of BritishColumbia School of Nursing, T201-2211 Wesbrook Mall, Vancouver, BC V6T2B5, Canada. 3Measurement Evaluation and Research Methods program,University of British Columbia, Vancouver, BC, Canada.Received: 16 October 2015 Accepted: 19 May 2016Homma et al. International Journal for Equity in Health  (2016) 15:79 Page 7 of 8References1. Saewyc EM. Research on adolescent sexual orientation: Development,health disparities, stigma and resilience. J Res Adolesc. 2011;21(1):256–72.2. 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Suicidality and depression disparitiesbetween sexual minority and heterosexual youth: A meta-analytic review. JAdolesc Health. 2011;49:115–23.11. Austin SB, Ziyadeh N, Fisher LB, Kahn JA, Colditz GA, Frazier AL. Sexualorientation and tobacco use in a cohort study of US adolescent girls andboys. Arch Pediatr Adolesc Med. 2004;158:317–22.12. Hagger Johnson G, Taibjee R, Semlyen J, Fitchie I, Fish J, Meads C, Varney J.Sexual orientation identity in relation to smoking history and alcohol use atage 18/19: cross-sectional associations from the Longitudinal Study ofYoung People in England (LSYPE). MJ Open. 2013;3:e002810. doi:10.1136/bmjopen-2013-002810.13. Busseri MA, Willoughby T, Chalmers H, Bogaert AF. On the associationbetween sexual attraction and adolescent risk behavior involvement:Examining mediation and moderation. Dev Psych. 2008;44(1):69–80.14. Saewyc E, Poon C, Wang N, Homma Y, Smith A, the McCreary CentreSociety. Not Yet Equal: The Health of Lesbian, Gay, & Bisexual Youth in BC.Vancouver, BC: McCreary Centre Society; 2007. ISBN #: 978-1-895438-84-5.15. Hurley M. Sexual orientation and legal rights: A chronological overview. PRB04-13E. Ottawa: Library of Parliament. Revised September 2005.16. Supreme Court of the United States of America, Obergefell v. Hodges, 576U.S. *****, No. 14–556. 2015.17. Russell ST, Kosciw J, Horn S, Saewyc E. Safe schools policy for LGBTQstudents. SRCD Social Policy Report. 2010;24(4):1–17.18. Lucassen MFG, Clark TC, Denny SJ, Fleming TM, Rossen FV, Sheridan J,Bullen P, Robinson EM. What has changed from 2001 to 2012 for sexualminority youth in New Zealand? J Paed Child Health. epub ahead of print2014, doi:10.1111/jpc.12727.19. Dick B, Ferguson J, Saewyc E, Baltag V, Bosek K, for the World HealthOrganization. Health for the World’s Adolescents: A Second Chance inthe Second Decade of Life. Geneva: World Health Organization; 2014.http://www.who.int/adolescent/second-decade.20. Allison PD. Comparing logit and probit coefficients across groups. SociolMethods Res. 1999;28:186–208.21. Altman DG, Bland JM. Interaction revisited: The difference between twoestimates. BMJ. 2003, 326:219. doi: http://dx.doi.org/10.1136/bmj.326.7382.219.22. Minnesota Departments of Education, Health, Human Services, & PublicSafety (2010). Minnesota Student Survey: 1992 – 2010 trends. Retrievedfrom http://www.health.state.mn.us/divs/chs/mss/trendreports/msstrendteport2010.pdf.23. Asada Y. On the choice of absolute or relative inequality measures. MilbankQ. 2010;88(4):612–22.24. Goodenow C, Szalacha LA, Robin LE, Westheimer K. Dimensions of sexualorientation and HIV-related risk among adolescent females: Evidence from astatewide survey. Am J Public Health. 2008;98(6):1051–8. doi:10.2105/AJPH.2005.080531.25. Igartua K, Thombs BD, Burgos G, Montoro R. Concordance and discrepancyin sexual identity, attraction, and behavior among adolescents. J AdolHealth. 2009;45:602–8. doi:10.1016/j.jadohealth.2009.03.019.26. Saewyc EM, Bauer GR, Skay CL, Bearinger LH, Resnick MD, Reis E, Murphy A.Measuring sexual orientation in adolescent health surveys: Evaluation ofeight school-based surveys. J Adol Health. 2004;35:345e. 1-e.16, on-line athttp://download.journals.elsevierhealth.com/pdfs/journals/1054-139X/PIIS1054139X04001612.pdf.•  We accept pre-submission inquiries •  Our selector tool helps you to find the most relevant journal•  We provide round the clock customer support •  Convenient online submission•  Thorough peer review•  Inclusion in PubMed and all major indexing services •  Maximum visibility for your researchSubmit your manuscript atwww.biomedcentral.com/submitSubmit your next manuscript to BioMed Central and we will help you at every step:Homma et al. International Journal for Equity in Health  (2016) 15:79 Page 8 of 8


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