Asymptotic properties of autoregressive integrated moving average processes

AbstractIn this paper we study the asymptotic behavior of so-called autoregressive integrated moving average processes. These processes constitute a large class of stochastic difference equations which includes among many other well-known processes the simple one-dimensional random walk. They were dubbed by G.E.P. Box and G.M. Jenkins who found them to provide useful models for studying and controlling the behavior of certain economic variables and various chemical processes. We show that autoregressive integrated moving average processes are asymptotically normally distributed, and that the sample paths of such processes satisfy a law of the iterated logarithm. We also establish a law which determines the time spent by a sample path on one or the other side of the “trend line” of the process

Rationality in Econometrics

The idea of rationality enters an econometrician's work in many ways; e.g., in his presuppositions about sample populations, in his model selections and data analyses, and in his choice of projects. I shall consider some of these ways and their ramifications for the econometrician's own life and for the development of econometrics. I begin with a discussion of rationality that I have found in the writings of Aristotle and other leading philosophers. My aim here is to establish the characteristics that we in good faith can expect rational members of a sample population to possess. The characteristics with which I end up have no definite meaning. Instead they are like undefined terms in mathematics that an econometrician can interpret in ways that suit the purposes of his research and seem appropriate for the population he is studying. When interpreted, the pertinent characteristics of the rational members of a given population become hypotheses whose empirical relevance must be tested. In rationally designed econometric studies the interpretation of 'rationality' that seems appropriate for a given study is usually an interpretation that the pertinent econometrician extracts from various economic theories. I look at some of these interpretations and discuss their empirical relevance. The interpretations of particular interest concern consumer choice under certainty, choice under risky and uncertain conditions, and choice in game-theoretic situations. These interpretations appear in various representations in the ways econometricians model rationality. I single out for discussion microeconometric models of consumer choice and macroeconometric rational expectations models. In the last section of the paper I consider two lacunas in Kuhn's and Lakatos' theories, and see how econometricians go about solving puzzles and extending positive heuristics. I begin by discussing the considerations that guide an econometrician in his choice of research projects. Then, I argue about the determinants of rational choice in model selection. Finally, I consider the politics of writing research reports. The contents of these sections concern aspects of an econometrician's rational choice that are relevant for the orderly development of econometrics.

Adjusting for outcome risk factors in immigrant datasets: total or direct effects?

Background When quantifying differences in health outcomes between immigrants and non-immigrants, it is common practice to adjust for observed differences in outcome risk factors between the groups being compared. However, as some of these outcome risk factors may act as mediators on the causal path between the exposure and outcome, adjusting for these may remove effects of factors that characterize the immigrants rather than removing a bias between immigrants and non-immigrants. Methods This study investigates the underlying conditions for which adjusting for outcome risk factors in regression models can lead to the estimation of either total or direct effect for the difference in health outcomes between immigrants and non-immigrants. For this investigation, we use modern tools in causal inference to construct causal models that we believe are highly relevant in an immigrant dataset. In these models, the outcome risk factor is modeled either as a mediator, a selection factor, or a combined mediator/selection factor. Unlike mediators, selection factors are variables that affect the probability of being in the immigrant dataset and may contribute to a bias when comparing immigrants and non-immigrants. Results When the outcome risk factor acts both as a mediator and selection factor, the adjustment for the risk factor in regression models leads to the estimation of what is known as a “controlled” direct effect. When the outcome risk factor is either a selection factor or a mediator alone, the adjustment for the risk factor in regression models leads to the estimation of a total effect or a controlled direct effect, respectively. In all regression analyses, also adjusting for various confounding paths, including mediator-outcome confounding, may be necessary to obtain valid controlled direct effects or total effects. Conclusions Depending on the causal role of the outcome risk factors in immigrant datasets, regression adjustment for these may result in the estimation of either total effects or controlled direct effects for the difference in outcomes between immigrants and non-immigrants. Because total and controlled direct effects are interpreted differently, we advise researchers to clarify to the readers which types of effects are presented when adjusting for outcome risk factors in immigrant datasets.publishedVersio

The Information Content of Commercial Paper Rating Downgrades: Further Evidence

Nayar received financial support from the Noble Foundation, and the Cooksey and Laird Programs. Both authors also thank the University of Oklahoma Research Council for other financial assistance. Comments from William Kross, Byung Ro, Mike Rozeff, Gregory Waymire, and participants at the University of Oklahoma Accounting and Finance Joint Workshop are appreciated. Eli Bartov (referee) helped to focus and strengthen the paper considerably. Stephanie Farewell, Giri Iyer, Alex Lee, Lori Mason, Karen Nunez, and Scott Whisenant provided valuable research assistance. Address correspondence to the authors at Michael F. Price College of Business, Adams Hall, University of Oklahoma, Norman, OK 73019–0450, Tel: (405) 325–5591.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Social differences in smoking and snuff use among Norwegian adolescents: A population based survey

<p>Abstract</p> <p>Background</p> <p>A change in pattern of tobacco use has been observed in the last decade in Norway. Snuff use and occasional smoking have to some degree replaced daily smoking among adolescents and young adults. Daily smoking is known to be negatively associated with social background factors, but little is known about these associations for other types of tobacco use. Our aim was to study different types of tobacco use among adolescents according to gender, educational ambitions, family background factors, and urbanization.</p> <p>Methods</p> <p>Cross-sectional, school-based study with 15 931 participants and response-rate 87%, conducted among 15 and 16 year olds during 2000–2004.</p> <p>Results</p> <p>More girls (33.8%) than boys (26.4%) were daily or occasional smokers, while more boys (21.4%) than girls (3.5%) were daily or occasional snuff users. Daily smoking was more common among adolescents planning vocational education, with single parents or poor family economy. Occasional smoking and snuff use (daily or occasionally) showed a similar, but less pronounced pattern regarding education and single parent families. Adolescents with parents from foreign countries were less likely to use tobacco. One exception was boys with parents from Muslim majority countries who had an increased risk of daily smoking. A typical combination user of both tobacco types was a Norwegian boy with divorced parents and ambitions to complete vocational studies or only one year of upper secondary school.</p> <p>Conclusion</p> <p>Tobacco use in adolescents is mainly associated with low educational ambitions and less affluent self-reported family economy. Adolescents with divorced parents use more tobacco than those living with both parents. Public health initiatives to avoid or reduce tobacco use should mainly target adolescents in vocational studies and those leaving school early.</p

Environmental toxicants in breast milk of Norwegian mothers and gut bacteria composition and metabolites in their infants at 1&nbsp;month.

BACKGROUND:Early disruption of the microbial community may influence life-long health. Environmental toxicants can contaminate breast milk and the developing infant gut microbiome is directly exposed. We investigated whether environmental toxicants in breastmilk affect the composition and function of the infant gut microbiome at 1&nbsp;month. We measured environmental toxicants in breastmilk, fecal short-chain fatty acids (SCFAs), and gut microbial composition from 16S rRNA gene amplicon sequencing using samples from 267 mother-child pairs in the Norwegian Microbiota Cohort (NoMIC). We tested 28 chemical exposures: polychlorinated biphenyls (PCBs), polybrominated flame retardants (PBDEs), per- and polyfluoroalkyl substances (PFASs), and organochlorine pesticides. We assessed chemical exposure and alpha diversity/SCFAs using elastic net regression modeling and generalized linear models, adjusting for confounders, and variation in beta diversity (UniFrac), taxa abundance (ANCOM), and predicted metagenomes (PiCRUSt) in low, medium, and high exposed groups. RESULTS:PBDE-28 and the surfactant perfluorooctanesulfonic acid (PFOS) were associated with less microbiome diversity. Some sub-OTUs of Lactobacillus, an important genus in early life, were lower in abundance in samples from infants with relative "high" (&gt; 80th percentile) vs. "low" (&lt; 20th percentile) toxicant exposure in this cohort. Moreover, breast milk toxicants were associated with microbiome functionality, explaining up to 34% of variance in acetic and propionic SCFAs, essential signaling molecules. Per one standard deviation of exposure, PBDE-28 was associated with less propionic acid (- 24% [95% CI - 35% to - 14%] relative to the mean), and PCB-209 with less acetic acid (- 15% [95% CI - 29% to - 0.4%]). Conversely, PFOA and dioxin-like PCB-167 were associated with 61% (95% CI 35% to 87%) and 22% (95% CI 8% to 35%) more propionic and acetic acid, respectively. CONCLUSIONS:Environmental toxicant exposure may influence infant gut microbial function during a critical developmental window. Future studies are needed to replicate these novel findings and investigate whether this has any impact on child health

Differences between the Norwegian and American business culture

Denne oppgaven handler om de kulturelle forskjellene mellom Norge og USA og om eventuelle utfordringer nordmenn kan oppleve ved etablering i det amerikanske markedet. I første del av oppgaven har jeg tatt for meg teori som jeg føler er relevant senere i oppgaven. Jeg tok først for meg det generelle begrepet ”kultur” for å finne ut av hva det egentlig. Videre tok jeg for meg kulturteorier fra Richard R. Gesteland, Edward T. Hall og Geert Hofstede. Deretter tok jeg for meg den amerikanske og norske forretningskulturen og knyttet disse opp mot hverandre. Neste steg var å velge metode. Jeg valgte å bruke kvalitativ metode med dybdeintervju fordi jeg ønsket å høre om folks erfaringer fra den amerikanske forretningskulturen. Jeg spurte fire respondenter som jeg visste hadde hver sin tilknytning og erfaring til USA. Da jeg analyserte respondentenes svar opp mot teorien så jeg at deres erfaringer samsvarte med teorien. Den norske og amerikanske forretningskulturen er ganske lik, men man ser også forskjeller og man må være forberedt noen utfordringer ved etablering i markedet.Sammendrag engelsk (abstract): This paper is about the cultural differences between Norway and the U.S. and if there is any challenges with establishing in the American business market. In the first part of the paper I looked at theory that I meant was relevant. I wrote about the general concept of culture to find out what it really means. After that, I wrote about different cultural theories from Richard R. Gesteland, Edward T. Hall and Geert Hofstede. Then I looked at the American and Norwegian business culture and made a comparison between the two cultures. The next step was for me to choose a research method and I chose a qualitative research method. The reason why I chose that method was because I wanted to hear about other peoples experiences in the American business culture. I asked four people that I knew had connections and experience for the U.S. In my analysis I saw that the respondents’ answers were consistent with the theory. The Norwegian and the American business culture is quite a like. Even so, you also can se differences and you should know that there will be some difficulties when establishing in the U.S. market

Domestic violence victimisation and its association with mental distress: A cross-sectional study of the Yangon Region, Myanmar

Objectives To estimate the prevalence of domestic violence, with subgroups of physical, sexual and emotional violence, among men and women and to assess the association between any lifetime domestic violence (DV) and mental distress among ever-married men and women. Design We conducted a cross-sectional study from October to November 2016 using a multistage sampling design. DV questionnaire was adopted from the Demographic and Health Survey programme. Mental distress was estimated using the Hopkins Symptom Checklist-10 (HSCL-10). HSCL-score and DV were the outcome and exposure variables, respectively, in multiple linear regression. Prevalence estimates and associations were presented with a 95% CI and the Wald test. Setting Urban and rural areas of the Yangon region, Myanmar. Participants Men and women ages 18 to 49 years were included. Institutionalised people, monks, nuns and individuals deemed too ill physically and/or mentally to participate were excluded. Results A random sample of 2383 people was included in the analyses. Among ever-married participants, lifetime (LT) and past-12-month (12M) prevalence of any domestic violence victimisation was higher in women compared with men: LT women: 61.8% (95% CI: 54.3 to 68.9) versus LT men: 42.4% (95% CI: 37.5 to 47.5) and 12M women: 51.2% (95% CI: 44.9 to 57.5) versus 12M men: 37.7% (95% CI: 32.9 to 42.7). Among never-married participants, lifetime physical and sexual violence victimisation rates was higher in men (34.3% and 7.9%) compared with women (19.1% and 6.4%). Mental distress was significantly associated with lifetime DV in women who were afraid of their husbands and men who had wives who exhibited controlling behaviours. Conclusions Domestic violence is prevalent among both men and women and is associated with mental distress. The findings highlight an urgent need to prevent domestic violence in both sexes, including through legal and policy reform and improved mental health services for DV victims.publishedVersio

Strong tuberculin response after BCG vaccination is associated with low multiple sclerosis risk: a population-based cohort study

Background: Multiple sclerosis (MS) is characterized by inflammatory lesions in the central nervous system involving pro-inflammatory T-cells. Immune dysregulation is well described in prevalent disease, but it is not known whether this precedes disease development. Bacillus Calmette–Guerin (BCG) vaccination ameliorates MS-like disease in mice. In people vaccinated with BCG, the tuberculin skin test (TST) offers a standardized measure of a T-cell-mediated immune response. We therefore hypothesized that the strength of the TST response after BCG vaccination is associated with subsequent MS risk. Methods: Using data from a Norwegian tuberculosis screening programme (1963–1975), we designed a population-based cohort study and related the size of TST reactions in individuals previously vaccinated with BCG to later MS disease identified through the Norwegian MS registry. We fitted Cox proportional hazard models and flexible parametric survival models to investigate the association between TST reactivity, MS risk and its temporal relationship. Results: Among 279 891 participants (52% females), 679 (69% females) later developed MS. Larger TST reactivity was associated with decreased MS risk. The hazard ratio for MS per every 4-mm increase in skin induration size was 0.86 (95% confidence interval 0.76–0.96) and similar between sexes. The strength of the association persisted for >30 years after the TST. Conclusion: A strong in vivo vaccine response to BCG is associated with reduced MS risk >30 years later. The immunological mechanisms determining TST reactivity suggest that skewed T-cell-mediated immunity precedes MS onset by many decades.publishedVersio