Psychiatric Morbidity Is Common Among Children With Juvenile Idiopathic Arthritis: A National Matched Cohort Study.

OBJECTIVE: Juvenile idiopathic arthritis (JIA) is a chronic rheumatic disease that causes joint inflammation and pain. Previous studies have indicated affected mental health and increased risk of psychiatric conditions among patients with JIA. We aimed to explore differences in psychiatric morbidity between children with JIA and their peers. We further studied if parental socioeconomic status (SES) influences the association between JIA and the risk of psychiatric morbidity. METHODS: We used a matched cohort design to estimate the association between JIA and psychiatric disease. Children with JIA, born between 1995 and 2014, were identified in Danish national registers. Based on birth registers, we randomly selected 100 age- and sex-matched children per index child. Index date was the date of the fifth JIA diagnosis code or the date of matching for reference children. End of follow-up was the date of psychiatric diagnosis, death, emigration, or December 31, 2018, whatever came first. Data were analyzed using a Cox proportional hazard model. RESULTS: We identified 2086 children with JIA with a mean age at diagnosis of 8.1 years. Children with JIA had a 17% higher instantaneous risk of a psychiatric diagnosis when compared with the reference group, with an adjusted hazard ratio of 1.17 (95% CI 1.02-1.34). Relevant associations were found only for depression and adjustment disorders. Stratifying our analysis for SES showed no modifying effect of SES. CONCLUSION: Children with JIA had a higher risk of psychiatric diagnoses compared to their peers, especially diagnoses of depression and adjustment disorders. The association between JIA and psychiatric disease did not depend on parental SES.

School Well-Being and Academic Performance of Children With Juvenile Idiopathic Arthritis: A National Register-Based Study.

OBJECTIVE: We aimed to investigate how school well-being (SWB) and academic performance of children with juvenile idiopathic arthritis (JIA) compare to their peers on a national level using the Danish national registers. Further, we investigated the potential influence of socioeconomic status (SES). METHODS: A population-wide, register-based, cross-sectional study was performed. We compared the results of children with and without JIA in the Danish National Well-Being Questionnaire (DNWQ), the National Danish School Testing (NDST), and their ninth grade (aged approximately 16 yrs) final school marks in Danish and mathematics. The results were analyzed using adjusted ordinal logistic regression (SWB) and linear regression (tests and marks). RESULTS: In separate cohorts, we included a total of 505,340 children answering the DNWQ, 812,461 children with NDST results, and the ninth-grade final marks of 581,804 children. Of these children, 1042, 1541, and 1410, respectively, fulfilled the criteria of JIA. Children with JIA reported SWB comparable to their peers, except for the question "Do you perform well in school?" (odds ratio 0.89, 95% CI 0.81-0.99). In the NDST, the children with JIA in general did just as well as their peers. We found no differences in the ninth-grade final marks in either Danish or mathematics. Stratifying the analyses on SES showed no significant differences in the associations. CONCLUSION: Overall, children with JIA report SWB comparable to that of children without JIA and perform equally well in school as children without JIA.

Outdoor Alternaria and Cladosporium spores and acute asthma.

BACKGROUND: Outdoor Alternaria and Cladosporium spores are ubiquitous. Few studies have assessed their impact on asthma hospitalizations providing conflicting results, mainly focused on vulnerable paediatric populations. We aimed to study the impact of outdoor Alternaria and Cladosporium concentrations on acute hospitalizations in the Capital Region of Denmark. METHODS: This is a bi-directional case-crossover study with 26 years of national registry data at individual level on acute asthma hospitalizations and daily average data on Alternaria and Cladosporium, pollen (Artemisia, Poaceae), maximal temperature, and air pollution. Conditional logistic regression models were applied to assess the associations. Concentration quartiles at lag 0 were used for categorizing the exposure. RESULTS: For lags 0-2, the odds of hospitalization were significantly higher for both Alternaria and Cladosporium at concentration quartile 2-4 compared with quartile 1. When stratified for age and sex, odds of hospitalization at Alternaria quartiles 2-4 were significantly higher in males below 40 years at lag 0-2, and at lag 0 in females (18-30 years), while quartiles 2-4 of Cladosporium concentrations were associated with significantly higher odds in boys (0-17 years) at lag 1-3, males (18-39 years) at lag 0-1, females (18-39 years) at lag 1-2, males (40-64 years) at lag 0-2, females (40-64 years) at lag 0 and 2, in seniors (65+ years) male at lag 1-2 and female at lag 0-1. The effect of Alternaria varied significantly depending on the level of Cladosporium (p < .0001). CONCLUSION: Ambient Alternaria and Cladosporium spores can induce asthma hospitalizations. Males are more susceptible to both genera. Males and females under age 40 years are more susceptible to Alternaria.

Chemometrics in Protein Formulation: Stability Governed by Repulsion and Protein Unfolding.

Therapeutic proteins can be challenging to develop due to their complexity and the requirement of an acceptable formulation to ensure patient safety and efficacy. To date, there is no universal formulation development strategy that can identify optimal formulation conditions for all types of proteins in a fast and reliable manner. In this work, high-throughput characterization, employing a toolbox of five techniques, was performed on 14 structurally different proteins formulated in 6 different buffer conditions and in the presence of 4 different excipients. Multivariate data analysis and chemometrics were used to analyze the data in an unbiased way. First, observed changes in stability were primarily determined by the individual protein. Second, pH and ionic strength are the two most important factors determining the physical stability of proteins, where there exists a significant statistical interaction between protein and pH/ionic strength. Additionally, we developed prediction methods by partial least-squares regression. Colloidal stability indicators are important for prediction of real-time stability, while conformational stability indicators are important for prediction of stability under accelerated stress conditions at 40 °C. In order to predict real-time storage stability, protein-protein repulsion and the initial monomer fraction are the most important properties to monitor.

Childhood socioeconomic position and cardiometabolic risk in young adulthood- the impact of mental health.

BACKGROUND: Low socioeconomic position in childhood is associated with greater cardiometabolic disease risk later in life. The aim of the current study is to examine the mediating impact of mental health on the association between childhood socioeconomic position and cardiometabolic disease risk in young adulthood. METHODS: We used a combination of national registers, longitudinal questionnaire-data and clinical measurements from a sub-sample (N = 259) of a Danish youth cohort. Childhood socioeconomic position was indicated by the educational level of the mother and the father at age 14. Mental health was measured by four different symptom scales at four age-points (age 15, 18, 21 and 28), and combined into one global score. Cardiometabolic disease risk was measured by nine biomarkers at age 28-30 and combined into one global score by sample-specific z-scores. We conducted analyses within the causal inference framework and evaluated the associations using nested counterfactuals. RESULTS: We found an inverse association between childhood socioeconomic position and cardiometabolic disease risk in young adulthood. The proportion of the association which was mediated by mental health was 10 (95% CI: -4; 24) % and 12 (95% CI: -4; 28) % using educational level of the mother and the father as indicator, respectively. CONCLUSIONS: Accumulated poorer mental health in childhood, youth and early adulthood partially explained the association between low childhood socioeconomic position and increased cardiometabolic disease risk in young adulthood. The results of the causal inference analyses rely on the underlying assumptions and correct depiction of the DAG. Since these are not all testable, we cannot exclude violations that potentially could bias the estimates. If the findings can be replicated, this would support a causal relationship and direct potentials for intervention. However, the findings point to a potential for intervention in young age in order to impede the translation of childhood social stratification into later cardiometabolic disease risk disparities.

Counterintuitive Electrostatics upon Metal Ion Coordination to a Receptor with Two Homotopic Binding Sites.

The consecutive binding of two potassium ions to a bis(18-crown-6) analogue of Tröger's base (BCETB) in water was studied by isothermal titration calorimetry using four different salts, KCl, KI, KSCN, and K2SO4. A counterintuitive result was observed: the enthalpy change associated with the binding of the second ion is more negative than that of the first (ΔHbind,2° < ΔHbind,1°). This remarkable finding is supported by continuum electrostatic theory as well as by atomic scale replica exchange molecular dynamics simulations, where the latter robustly reproduces experimental trends for all simulated salts, KCl, KI, and KSCN, using multiple force fields. While an enthalpic K+-K+ attraction in water poses a small, but fundamentally important, contribution to the overall interaction, the probability of the collapsed conformation (COL) of BCETB, where both crown ether moieties (CEs) of BCETB are bent in toward the cavity, was found to increase successively upon binding of the first and second potassium ions. The promotion of the COL conformation reveals favorable intrinsic interactions between the potassium coordinated CEs, which further contribute to the observation that ΔHbind,2° < ΔHbind,1°. While the observed trend is independent of the counterion, the origin of the significantly larger magnitude of the difference ΔHbind,2° - ΔHbind,1° observed experimentally for KSCN was studied in light of the weaker hydration of the thiocyanate anion, resulting in an enrichment of thiocyanate ions close to BCETB compared to the other studied counterions.

Anion-cation contrast of small molecule solvation in salt solutions.

The contributions from anions and cations from salt are inseparable in their perturbation of molecular systems by experimental and computational methods, rendering it difficult to dissect the effects exerted by the anions and cations individually. Here we investigate the solvation of a small molecule, caffeine, and its perturbation by monovalent salts from various parts of the Hofmeister series. Using molecular dynamics and the energy-representation theory of solvation, we estimate the solvation free energy of caffeine and decompose it into the contributions from anions, cations, and water. We also decompose the contributions arising from the solute-solvent and solute-ions interactions and that from excluded volume, enabling us to pin-point the mechanism of salt. Anions and cations revealed high contrast in their perturbation of caffeine solvation, with the cations salting-in caffeine via binding to the polar ketone groups, while the anions were found to be salting-out via perturbations of water. In agreement with previous findings, the perturbation by salt is mostly anion dependent, with the magnitude of the excluded-volume effect found to be the governing mechanism. The free-energy decomposition as conducted in the present work can be useful to understand ion-specific effects and the associated Hofmeister series.

Temporal and regional differences in the incidence of hospital-diagnosed endometriosis: a Danish population-based study.

INTRODUCTION: Due to diagnostic challenges, normalization of symptoms and an overall lack of awareness among both patients and physicians, endometriosis is an underdiagnosed disease. This can result in delayed treatment and potentially worsening of the disease. Despite initiatives, such as patients' support organizations and specialized endometriosis referral centers, differences in awareness, socioeconomic factors and lifestyle, combined with varying distances to specialized referral centers, could result in regional differences in the degree of underdiagnosing. This study aims to explore temporal and regional variations in the incidence of endometriosis based on the Danish hospital discharge register, and shed light on the degree of underdiagnosing of endometriosis in Denmark. MATERIAL AND METHODS: This registry-based cohort study included all women aged 15-55 living in Denmark from 1990-2017. Participants were identified through the Danish Civil Registration system and endometriosis diagnoses received at a hospital were obtained from the Danish National Patient Registry. Incidence rates of diagnosed endometriosis were calculated for each year of the study period and for each municipality in Denmark. A Cox regression analysis, stratified by calendar time and adjusted for ethnic origin, household composition, highest educational level and family socioeconomic status, was performed to estimate the association between residence and likelihood of receiving a hospital-based diagnosis of endometriosis. RESULTS: The nationwide incidence rate of hospital-diagnosed endometriosis was 7.89 (95% confidence interval [CI] 7.80-7.99) per 10 000 person-years and the prevalence in 2017 was 1.63%. The results showed an overall increase in the incidence of diagnosed endometriosis of 46.8% (95% CI 32.9-62.2) during the study period and also displayed significant regional differences. After adjustments, women living in northern Jutland had the highest probability of receiving a hospital-based diagnosis of endometriosis (hazard ratio 1.13, 95% CI 1.09-1.18), whereas women living in northern Zealand had the lowest probability (hazard ratio 0.63, 95% CI 0.60-0.67) compared with eastern Jutland. These regional differences have become more evident over time. CONCLUSIONS: Our results reveal significant regional differences in the incidence of hospital-diagnosed endometriosis, suggesting that a significant number of women may be left behind without a diagnosis. Further studies are needed to assess the underlying reasons for the significant regional differences.

Pre-adolescents with multiple health complaints redeem more prescriptions: A follow-up study in the Danish National Birth Cohort.

Aims: This study aimed to examine the association between multiple health complaints (MHC) in pre-adolescence and prescription redemption in adolescence. Methods: This was a nationwide population-based study based on the Danish National Birth Cohort for an average of 6.9 years (2010-2018). A total of 96,382 children were invited at the age of 11. A modified version of the Health Behaviour in School Children Symptom Checklist was dichotomised into the World Health Organization's definition of MHC (⩾2 complaints, each with a frequency of at least weekly, yes/no). The number of prescriptions was retrieved from Danish registries. Negative binomial regression estimated incidence rate ratios (IRRs) comparing children with MHC to children without. Prescription redemption was further stratified by psychiatric/somatic medication and into subtypes of prescriptions. Results: A total of 47,365 (49.1%) children participated (Mage=11.2 years, 52% girls). MHC were reported by 10.3%. The unadjusted IRR (MHC vs. no MHC) of all types of redemptions was 1.57 (95% confidence interval (CI) 1.49-1.64). Results were robust to adjustment for socio-demographic variables and somatic/psychiatric morbidity at baseline (IRR=1.47; 95% CI 1.40-1.54). Associations were especially strong for psychiatric medication (adjusted IRR=3.88; 95% CI 3.43-4.40) and were modified by neither sex nor maternal education. Conclusions: MHC in pre-adolescents predict prescription redemption. This implies that changes in MHC might be indicative of changes in public health. This requires further study, as the cause of a change in reporting of symptoms might also cause a change in treatment response. The latter determines whether prescriptions are treating ill-being or needlessly medicalising subjective symptoms.

Charge Interactions in a Highly Charge-Depleted Protein.

Electrostatic forces are important for protein folding and are favored targets of protein engineering. However, interactions between charged residues are difficult to study because of the complex network of interactions found in most proteins. We have designed a purposely simple system to investigate this problem by systematically introducing individual and pairs of charged and titratable residues in a protein otherwise free of such residues. We used constant pH molecular dynamics simulations, NMR spectroscopy, and thermodynamic double mutant cycles to probe the structure and energetics of the interaction between the charged residues. We found that the partial burial of surface charges contributes to a shift in pKa value, causing an aspartate to titrate in the neutral pH range. Additionally, the interaction between pairs of residues was found to be highly context dependent, with some pairs having no apparent preferential interaction, while other pairs would engage in coupled titration forming a highly stabilized salt bridge. We find good agreement between experiments and simulations and use the simulations to rationalize our observations and to provide a detailed mechanistic understanding of the electrostatic interactions.

Impact of Arginine-Phosphate Interactions on the Reentrant Condensation of Disordered Proteins.

Re-entrant condensation results in the formation of a condensed protein regime between two critical ion concentrations. The process is driven by neutralization and inversion of the protein charge by oppositely charged ions. Re-entrant condensation of cationic proteins by the polyvalent anions, pyrophosphate and tripolyphosphate, has previously been observed, but not for citrate, which has similar charge and size compared to the polyphosphates. Therefore, besides electrostatic interactions, other specific interactions between the polyphosphate ions and proteins must contribute. Here, we show that additional attractive interactions between arginine and tripolyphosphate determine the re-entrant condensation and decondensation boundaries of the cationic, intrinsically disordered saliva protein, histatin 5. Furthermore, we show by small-angle X-ray scattering (SAXS) that polyvalent anions cause compaction of histatin 5, as would be expected based solely on electrostatic interactions. Hence, we conclude that arginine-phosphate-specific interactions not only regulate solution properties but also influence the conformational ensemble of histatin 5, which is shown to vary with the number of arginine residues. Together, the results presented here provide further insight into an organizational mechanism that can be used to tune protein interactions in solution of both naturally occurring and synthetic proteins.

Five-year outcomes of ADHD diagnosed in adulthood.

There is a dearth of long-term follow-up studies of adults diagnosed with ADHD. Here, the aim was to evaluate long-term outcomes in a group of ADHD patients diagnosed in adulthood and receiving routine psychiatric health care. Adults diagnosed with any type of ADHD (n = 52) and healthy controls (n = 73) were assessed at baseline and at a 5-year follow-up, using Global Assessment of Functioning (GAF), Clinical Global Impression (CGI), Brown ADD Scale (BADDS) and Adult ADHD Self-Report Scale (ASRS). A multivariate regression method was used to identify factors predicting 5-year outcomes, including baseline ratings, medication intensity, comorbidity, intelligence quotient (IQ), age, and sex. After 5 years, ADHD patients reported fewer and/or less severe symptoms compared to baseline, but remained at clinically significant symptom levels and with functional deficits. Baseline self-reports of ADHD symptoms predicted their own 5-year outcome and low baseline functioning level predicted improved global functioning at follow-up. Factors previously reported to predict short-term outcomes (i.e., medication, comorbidity, IQ, age, and sex) did not anticipate long-term outcomes in present study.

Total Description of Intrinsic Amphiphile Aggregation: Calorimetry Study and Molecular Probing.

Isothermal titration calorimetry (ITC) is an apt tool for a total thermodynamic description of self-assembly of atypical amphiphiles such as anionic boron cluster compounds (COSAN) in water. Global fitting of ITC enthalpograms reveals remarkable features that differentiate COSAN from classical amphiphiles: (i) strong enthalpy and weak entropy contribution to the free energy of aggregation, (ii) low degree of counterion binding, and (iii) very low aggregation number, leading to deviations from the ideal closed association model. The counterion condensation obtained from the thermodynamic model was compared with the results of 7Li DOSY NMR of Li[COSAN] micelles, which allows direct tracking of Li cations. The basic thermodynamic study of COSAN alkaline salt aggregation was complemented by NMR and ITC experiments in dilute Li/NaCl and acetonitrile aqueous solutions of COSAN. The strong affinity of acetonitrile molecules to COSAN clusters was microscopically investigated by all-atomic molecular dynamics simulations. The impact of ionic strength on COSAN self-assembling was comparable to the behavior of classical amphiphiles, whereas even a small amount of acetonitrile cosolvent has a pronounced nonclassical character of COSAN aggregation. It demonstrates that large self-assembling changes are triggered by traces of organic solvents.

Estimating a population cumulative incidence under calendar time trends.

BACKGROUND: The risk of a disease or psychiatric disorder is frequently measured by the age-specific cumulative incidence. Cumulative incidence estimates are often derived in cohort studies with individuals recruited over calendar time and with the end of follow-up governed by a specific date. It is common practice to apply the Kaplan-Meier or Aalen-Johansen estimator to the total sample and report either the estimated cumulative incidence curve or just a single point on the curve as a description of the disease risk. METHODS: We argue that, whenever the disease or disorder of interest is influenced by calendar time trends, the total sample Kaplan-Meier and Aalen-Johansen estimators do not provide useful estimates of the general risk in the target population. We present some alternatives to this type of analysis. RESULTS: We show how a proportional hazards model may be used to extrapolate disease risk estimates if proportionality is a reasonable assumption. If not reasonable, we instead advocate that a more useful description of the disease risk lies in the age-specific cumulative incidence curves across strata given by time of entry or perhaps just the end of follow-up estimates across all strata. Finally, we argue that a weighted average of these end of follow-up estimates may be a useful summary measure of the disease risk within the study period. CONCLUSIONS: Time trends in a disease risk will render total sample estimators less useful in observational studies with staggered entry and administrative censoring. An analysis based on proportional hazards or a stratified analysis may be better alternatives.

Personality traits in bipolar disorder and influence on outcome.

BACKGROUND: The aim was to investigate the personality profile of bipolar disorder I and II, and healthy controls, and to study whether personality influences the course of bipolar disorder. METHODS: One hundred ten patients with bipolar disorder I, 85 patients with bipolar disorder II, and 86 healthy individuals had their personality profile assessed using the Swedish universities Scales of Personality (SSP), an instrument developed to explore personality-related vulnerabilities and correlates of psychiatric disorders. Patients were followed prospectively for 2 years. To assess the impact of Neuroticism, Aggressiveness, and Disinhibition on illness course, we performed logistic regressions with the outcome variables mood episodes (depressive, hypo/manic, mixed), suicide attempts, violence, and the number of sick leave days. RESULTS: Bipolar disorder I and II demonstrated higher global measures of Neuroticism, Aggressiveness, and Disinhibition as compared with healthy controls. A third of the patients scored ≥1 SD above the population-based normative mean on the global neuroticism measure. The two subtypes of bipolar disorder were, however, undistinguishable on all of the personality traits. In the unadjusted model, higher neuroticism at baseline predicted future depressive episodes and suicide attempts/violent behavior, but this association disappeared when adjusting for baseline depressive symptoms as assessed with MADRS. CONCLUSIONS: A significant minority of the patients scored ≥1 SD above the population mean on the global measures of Neuroticism, Aggressiveness and Disinhibition; scores this high are usually evident clinically. Yet, the personality profile does not seem to have prognostic value over a 2-year period.

Classification of cognitive performance in bipolar disorder.

OBJECTIVE: To understand the etiology of cognitive impairment associated with bipolar disorder, we need to clarify potential heterogeneity in cognitive functioning. To this end, we used multivariate techniques to study if the correlation structure of cognitive abilities differs between persons with bipolar disorder and controls. METHOD: Clinically stable patients with bipolar disorder (type I: n = 64; type II: n = 44) and healthy controls (n = 86) were assessed with a wide range of cognitive tests measuring executive function, speed, memory, and verbal skills. Data were analysed with multivariate techniques. RESULTS: A distinct subgroup (∼30%) could be identified that performed significantly poorer on tests concerning memory function. This cognitive phenotype subgroup did not differ from the majority of bipolar disorder patients with respect to other demographic or clinical characteristics. CONCLUSIONS: Whereas the majority of patients performed similar to controls, a subgroup of patients with bipolar disorder differed substantially from healthy controls in the correlation pattern of low-level cognitive abilities. This suggests that cognitive impairment is not a general trait in bipolar disorder but characteristic of a cognitive subgroup. This has important clinical implications for cognitive rehabilitation and remediation.

Zucker diabetic fatty rats, a model for type 2 diabetes, develop an inner ear dysfunction that can be attenuated by losartan treatment.

Hearing loss secondary to diabetes remains under debate. In our study, we used Zucker Diabetic Fatty (ZDF) rats as an animal model of type 2 diabetes to investigate whether (1) hearing ability impairment and structural alterations of the inner ear occur in diabetes and (2) an angiotensin II receptor blocker (losartan) can protect rats from diabetic damage. Homozygous mutants were treated with a placebo or losartan and heterozygous animals served as non-diabetic controls. All animals underwent immunohistochemical and electronmicroscopical analysis. Functional testing of hearing ability was performed by click-evoked auditory brainstem responses. The present study showed significant sensorineural hearing impairment in placebo-treated diabetic rats (hearing threshold, 45.0 ± 2.1 dB SPL) compared to both non-diabetic controls (34.7 ± 4 dB SPL) and losartan-treated diabetic rats (36.1 ± 7.4 dB SPL). Concurrently, the functional decline in the placebo-treated rats was associated with significant morphological abnormalities, particularly in the intermediate cells of the stria vascularis and with strial dysfunction. These degenerative changes were indicated by the down-regulation of several pumps, ionic and cellular channels, which are involved in the cycling of K(+) and the maintenance of the endocochlear potential essential for the hearing process. Thus, the inner ear can be regarded as a target organ during hyperglycemic disorders and a metabolically induced "diabetic otopathy" may be added to angiopathy, nephropathy and neuropathy as a specific complication of diabetes mellitus. Blockade of the angiotensin II receptor can prevent this "diabetic otopathy" despite hyperglycemic serum levels.

The increasing prevalence of reported diagnoses of childhood psychiatric disorders: a descriptive multinational comparison.

The objective of this study is to compare the time trend of reported diagnoses of autism spectrum disorder (ASD), hyperkinetic disorder, Tourette's syndrome, and obsessive-compulsive disorder across four countries after standardizing the study period, diagnostic codes used to define the conditions and statistical analyses across countries. We use a population-based cohort, including all live-born children in Denmark, Finland, Sweden and Western Australia, from January 1, 1990, through December 31, 2007 and followed through December 31, 2011. The main outcome measure is age-specific prevalence of diagnoses reported to population-based registry systems in each country. We observe an increase in age-specific prevalence for reported diagnoses of all four disorders across birth-year cohorts in Denmark, Finland, Sweden, and (for ASD) Western Australia. Our results highlight the increase in the last 20 years in the number of children and families in contact with health care systems for diagnosis and services for an array of childhood neuropsychiatric disorders, a phenomenon not limited to ASD. Also, the age of diagnosis of the studied disorders was often much higher than what is known of the typical age of onset of symptoms, and we observe limited leveling off in the incidence rate with increasing age.

Events per variable for risk differences and relative risks using pseudo-observations.

A method based on pseudo-observations has been proposed for direct regression modeling of functionals of interest with right-censored data, including the survival function, the restricted mean and the cumulative incidence function in competing risks. The models, once the pseudo-observations have been computed, can be fitted using standard generalized estimating equation software. Regression models can however yield problematic results if the number of covariates is large in relation to the number of events observed. Guidelines of events per variable are often used in practice. These rules of thumb for the number of events per variable have primarily been established based on simulation studies for the logistic regression model and Cox regression model. In this paper we conduct a simulation study to examine the small sample behavior of the pseudo-observation method to estimate risk differences and relative risks for right-censored data. We investigate how coverage probabilities and relative bias of the pseudo-observation estimator interact with sample size, number of variables and average number of events per variable.

Free-energy decomposition of salt effects on the solubilities of small molecules and the role of excluded-volume effects.

The roles of cations and anions are different in the perturbation on solvation, and thus, the analyses of the separated contributions from cations and anions are useful to establish molecular pictures of ion-specific effects. In this work, we investigate the effects of cations, anions, and water separately in the solvation of n-alcohols and n-alkanes by free-energy decomposition. By utilising energy-representation theory of solvation, we address the contributions arising from the direct solute-solvent interactions and the excluded-volume effects. It is found that the change in solvation of n-alcohols and n-alkanes upon addition of salt depends primarily on the anion species. The direct interaction between the anion and solute is in agreement with the Setschenow coefficient in terms of the ranking of salting-in and salting-out for n-alkanes, which corresponds to the extent of accumulation of the anion on the solute surface. For each of the n-alcohols and n-alkanes examined, the excluded-volume component in the Setschenow coefficient is well correlated to the (total) Setschenow coefficient when the salt effects are concerned. The ranking of the excluded-volume component in the variation of the salt species is parallel to the water contribution, which is correlated further to the change in the water density upon the addition of the salt.