Diagnosing and Handling Common Violations of Missing at Random.

Ignorable likelihood (IL) approaches are often used to handle missing data when estimating a multivariate model, such as a structural equation model. In this case, the likelihood is based on all available data, and no model is specified for the missing data mechanism. Inference proceeds via maximum likelihood or Bayesian methods, including multiple imputation without auxiliary variables.

Ignoring Non-ignorable Missingness.

The classical missing at random (MAR) assumption, as defined by Rubin (Biometrika 63:581-592, 1976), is often not required for valid inference ignoring the missingness process. Neither are other assumptions sometimes believed to be necessary that result from misunderstandings of MAR. We discuss three strategies that allow us to use standard estimators (i.

The Role of Conditional Likelihoods in Latent Variable Modeling.

In psychometrics, the canonical use of conditional likelihoods is for the Rasch model in measurement. Whilst not disputing the utility of conditional likelihoods in measurement, we examine a broader class of problems in psychometrics that can be addressed via conditional likelihoods. Specifically, we consider cluster-level endogeneity where the standard assumption that observed explanatory variables are independent from latent variables is violated.

Parental income and mental disorders in children and adolescents: prospective register-based study.

Background: Children with low-income parents have a higher risk of mental disorders, although it is unclear whether other parental characteristics or genetic confounding explain these associations and whether it is true for all mental disorders.

Methods: In this registry-based study of all children in Norway (n = 1 354 393) aged 5-17 years from 2008 to 2016, we examined whether parental income was associated with childhood diagnoses of mental disorders identified through national registries from primary healthcare, hospitalizations and specialist outpatient services.

Results: There were substantial differences in mental disorders by parental income, except for eating disorders in girls.

A Dyadic IRT Model.

We propose a dyadic Item Response Theory (dIRT) model for measuring interactions of pairs of individuals when the responses to items represent the actions (or behaviors, perceptions, etc.) of each individual (actor) made within the context of a dyad formed with another individual (partner). Examples of its use include the assessment of collaborative problem solving or the evaluation of intra-team dynamics.

A Constrained Metropolis-Hastings Robbins-Monro Algorithm for Q Matrix Estimation in DINA Models.

In diagnostic classification models (DCMs), the Q matrix encodes in which attributes are required for each item. The Q matrix is usually predetermined by the researcher but may in practice be misspecified which yields incorrect statistical inference. Instead of using a predetermined Q matrix, it is possible to estimate it simultaneously with the item and structural parameters of the DCM.

Seasonal and pandemic influenza during pregnancy and risk of fetal death: A Norwegian registry-based cohort study.

Previous studies of fetal death with maternal influenza have been inconsistent. We explored the effect of maternal influenza-like illness (ILI) in pregnancy on the risk of fetal death, distinguishing between diagnoses during regular influenza seasons and the 2009/2010 pandemic and between trimesters of ILI. We used birth records from the Medical Birth Registry of Norway to identify fetal deaths after the first trimester in singleton pregnancies (2006-2013).

Pairwise residuals and diagnostic tests for misspecified dependence structures in models for binary longitudinal data.

Maximum likelihood estimation of models for binary longitudinal data is typically inconsistent if the dependence structure is misspecified. Unfortunately, diagnostics specifically designed for detecting such misspecifications are scant. We develop residuals and diagnostic tests based on comparing observed and expected frequencies of response patterns over time in the presence of arbitrary time-varying and time-invariant covariates.

The transition model test for serial dependence in mixed-effects models for binary data.

Generalized linear mixed models for longitudinal data assume that responses at different occasions are conditionally independent, given the random effects and covariates. Although this assumption is pivotal for consistent estimation, violation due to serial dependence is hard to assess by model elaboration. We therefore propose a targeted diagnostic test for serial dependence, called the transition model test (TMT), that is straightforward and computationally efficient to implement in standard software.

A competing risks approach to "biologic" interaction.

In epidemiology, the concepts of "biologic" and "statistical" interactions have been the subject of extensive debate. We present a new approach to biologic interaction based on Rothman's original (Am J Epidemiol, 104:587-592, 1976) discussion of sufficient causes. We do this in a probabilistic framework using competing risks and argue that sufficient cause interaction between two factors can be evaluated via the parameters in a particular statistical model, the additive hazard rate model.

Risk of fetal death after pandemic influenza virus infection or vaccination.

Background: During the 2009 influenza A (H1N1) pandemic, pregnant women were at risk for severe influenza illness. This concern was complicated by questions about vaccine safety in pregnant women that were raised by anecdotal reports of fetal deaths after vaccination.

Methods: We explored the safety of influenza vaccination of pregnant women by linking Norwegian national registries and medical consultation data to determine influenza diagnosis, vaccination status, birth outcomes, and background information for pregnant women before, during, and after the pandemic.

Musculoskeletal pain and overuse syndromes in adult acquired major upper-limb amputees.

Objectives: (1) To compare the prevalence of self-reported musculoskeletal pain in upper-limb amputees (ULAs) in Norway with that of a control group drawn from the Norwegian general population; (2) to describe musculoskeletal pain bothersomeness in ULAs; (3) to estimate the association between prosthesis wear and self-reported musculoskeletal pain in ULAs; and (4) to describe the occurrence of musculoskeletal overuse syndromes in a sample of ULAs.

Design: Cross-sectional study: postal questionnaires and clinical examinations.

Setting: Norwegian ULA population.

Assessing physical function in adult acquired major upper-limb amputees by combining the Disabilities of the Arm, Shoulder and Hand (DASH) Outcome Questionnaire and clinical examination.

Objectives: To describe physical function in adult acquired major upper-limb amputees (ULAs) by combining self-assessed arm function and physical measures obtained by clinical examinations; to estimate associations between background factors and self-assessed arm function in ULAs; and to assess whether clinical examination findings may be used to detect reduced arm function in unilateral ULAs.

Survey: postal questionnaires and clinical examinations.

Setting: Norwegian ULA population.

Classical latent variable models for medical research.

Latent variable models are commonly used in medical statistics, although often not referred to under this name. In this paper we describe classical latent variable models such as factor analysis, item response theory, latent class models and structural equation models. Their usefulness in medical research is demonstrated using real data.

A simulation study of three methods for detecting disease clusters.

Background: Cluster detection is an important part of spatial epidemiology because it can help identifying environmental factors associated with disease and thus guide investigation of the aetiology of diseases. In this article we study three methods suitable for detecting local spatial clusters: (1) a spatial scan statistic (SaTScan), (2) generalized additive models (GAM) and (3) Bayesian disease mapping (BYM). We conducted a simulation study to compare the methods.

Likelihood ratio tests in behavioral genetics: problems and solutions.

The likelihood ratio test of nested models for family data plays an important role in the assessment of genetic and environmental influences on the variation in traits. The test is routinely based on the assumption that the test statistic follows a chi-square distribution under the null, with the number of restricted parameters as degrees of freedom. However, tests of variance components constrained to be non-negative correspond to tests of parameters on the boundary of the parameter space.

Early respiratory infections, asthma, and allergy: 10-year follow-up of the Oslo Birth Cohort.

Objective: It has been hypothesized that early infections protect against the development of atopic disease, but there have been few long-term follow-up studies. We estimated the associations between early respiratory infections and doctor-diagnosed asthma, allergic rhinitis, and skin-prick sensitization in children at 10 years of age in the Oslo Birth Cohort, established in 1992-1993. We also considered birth order and attendance at a child care center as proxy measures of increased exposure to infections early in life.

Recurrent risk of anal sphincter laceration among women with vaginal deliveries.

Objective: The first aim of this study was to estimate the impact of anal sphincter laceration during the first delivery on the risk of recurrence in the second delivery. The second aim was to estimate the absolute risk of anal sphincter laceration in the second delivery according to the history of anal sphincter laceration and birth weight.

Methods: In this population-based cohort study, the study sample comprised all women included in the Norwegian Medical Birth Registry with 2 consecutive singleton vaginal deliveries during the period 1967-1998 (n = 486,463).

The importance of social characteristics of communities for the medically based disability pension.

Background: The aim of this study was to look for any possible contextual effect of deprivation at municipality level on the risk of being granted the medically based disability pension, controlled for compositional effects due to spatial concentration of people with a high risk of disability.

Methods: The material consists of the residentiary part of a total Norwegian county population aged 20-54 years without disability pension at baseline, n=40,083. This study was performed as a 10-year follow-up study.

Recurrence risk of preeclampsia in twin and singleton pregnancies.

The etiology of preeclampsia is unknown. The relatively high risk of recurrence of preeclampsia in subsequent pregnancies to the same mother suggests a genetic basis for the disease, but the mode of inheritance is uncertain. We compare the risk of preeclampsia in second pregnancies for mothers whose first preeclamptic pregnancy was either a singleton or a twin pregnancy.

A comparison of anxiety and depressive symptomatology in postpartum and non-postpartum mothers.

Background: The aim of the study was to compare the distribution of symptoms of anxiety and depression among postpartum as compared with non-postpartum mothers, and to estimate the impact of the postpartum period on the risk of anxiety and depression when adjusted for other risk factors.

Methods: A questionnaire survey approaching all women 18-40 years of age in two municipalities in Norway during the period 1998-1999 was conducted. A total of 2,730 women were included, of whom 416 were in the postpartum period.

Traffic related air pollution and acute hospital admission for respiratory diseases in Drammen, Norway 1995-2000.

The aim of this study was to estimate the associations between seven ambient air pollutants [particulate matter (PM10), nitrous dioxide (NO2), sulfur dioxide (SO2), ozone (O3), benzene, formaldehyde and toluene] and acute hospital admissions for respiratory diseases in Drammen, Norway 1995-2000. Time-series analysis of counts was performed by means of generalized additive models with log link and Poisson distribution. The results showed that benzene was the pollutant having the strongest association with respiratory diseases for the total study period, the relative risk of an interquartile increase of benzene was 1.