Bakgrund: Tobaksrökning är idag ett utbrett folkhälsoproblem och den främsta orsaken till sjukdom och död inom den Europeiska Unionen. I Sverige börjar 15 000 ungdomar röka varje år och flickor är rökare i större utsträckning än pojkar. Syfte: Syftet med denna studie var att beskriva ungdomars orsaker till och erfarenheter av tobaksrökning ur ett psykosocialt perspektiv. Metod: För att besvara syftet gjordes en litteraturstudie som baserades på systematisk, metodisk och kritisk granskning av tidigare publicerat material inom området. Artikelsökning gjordes i databaserna PubMed, SciVerse, Psycinfo och Cinahl och begränsades till publikationsår 1995-2011. Arton stycken artiklar användes och målgruppen var ungdomar mellan 11 och 18 år.            Resultat: Ungdomars orsaker till och erfarenheter av tobaksrökning presenterades i fyra temaområden: Ungdomars attityd och självförtroende, Tobaksrökning vid stress och problem, Den sociala omgivningens betydelse och Tillgång till cigaretter. Ungdomars relation till rökning påverkades av den sociala omgivningen och tillgången till cigaretter. Ungdomar rökte för att hantera olika situationer i livet, framförallt för att öka sin sociala status men också för att uppnå psykiskt välbefinnande. Föräldrar, syskon och kamrater hade starka samband med att ungdomar rökte och införskaffandet av cigaretter innebar inga svårigheter för de minderåriga ungdomarna. Implikation: Det är viktigt att ha kunskap om varför ungdomar börjar röka och fortsätter. Denna studie ger en översikt över problemet och kan därmed vara användbar vid framtida folkhälsoarbeten för att öka de positiva effekterna av insatserna samt vid vidare forskning kring relationen mellan stress och rökning.

In this thesis, we explore two different approaches to causal inferences. The traditional approach models the theoretical relationship between the outcome variables and their explanatory variables, i.e., the science, at the same time as the systematic differences between treated and control subjects are modeled, i.e., the assignment mechanism. The alternative approach, based on Rubin's Causal Model (RCM), makes it possible to model the science and the assignment mechanism separately in a two-step procedure. In the first step, no outcome variables are used when the assignment mechanism is modeled, the treated students are matched with similar control students using this mechanism, and the models for the science are determined. Outcome variables are only used in the second step when these pre-specified models for the science are fitted. In the first paper, we use the traditional approach to evaluate whether a husband is more prone to quit smoking when his wife quits smoking than he would have been had his wife not quit. We find evidence that this is the case, but that our analysis must rely on restrictive assumptions. In the subsequent two papers, we use the alternative RCM approach to evaluate if a Harvard freshman who does not smoke (observed potential outcome) is more prone to start smoking when he shares a suite with at least one smoker, than he would have been had he shared a suite with only smokers (missing potential outcomes). We do not find evidence that this is the case, and the small and insignificant treatment effect is robust against various assumptions that we make regarding covariate adjustments and missing potential outcomes. In contrast, we do find such evidence when we use the traditional approach previously used in the literature to evaluate peer effects relating to smoking, but the treatment effect is not robust against the assumptions that we make regarding covariate adjustments. These contrasting results in the two latter papers allow us to conclude that there are a number of advantages with the alternative RCM approach over the traditional approaches previously used to evaluate peer effects relating to smoking. Because the RCM does not use the outcome variables when the assignment mechanism is modeled, it can be re-fit repeatedly without biasing the models for the science. The assignment mechanism can then often be modeled to fit the data better and, because the models for the science can consequently better control for the assignment mechanism, they can be fit with less restrictive assumptions. Moreover, because the RCM models two distinct processes separately, the implications of the assumptions that are made on these processes become more transparent. Finally, the RCM can derive the two potential outcomes needed for drawing causal inferences explicitly, which enhances the transparency of the assumptions made with regard to the missing potential outcomes. / Diss. Stockholm : Handelshögskolan, 2006 S. 1-13: sammanfattning, s. [15]-161: 4 uppsatser