Tests for stochastic ordering under biased sampling

In two-sample comparison problems it is often of interest to examine whether one distribution function majorizes the other, i.e., for the presence of stochastic ordering. This paper develops a nonparametric test for stochastic ordering from size-biased data, allowing the pattern of the size bias to differ between the two samples. The test is formulated in terms of a maximally-selected local empirical likelihood statistic. A Gaussian multiplier bootstrap is devised to calibrate the test. Simulation results show that the proposed test outperforms an analogous Wald-type test, and that it provides substantially greater power over ignoring the size bias. The approach is illustrated using data on blood alcohol concentration of drivers involved in car accidents, where the size bias is due to drunker drivers being more likely to be involved in accidents. Further, younger drivers tend to be more affected by alcohol, so in making comparisons with older drivers the analysis is adjusted for differences in the patterns of size bias.

Prenatal Nicotine Exposure and Risk of Schizophrenia Among Offspring in a National Birth Cohort

OBJECTIVE

Cigarette smoking during pregnancy is a major public health problem leading to adverse health outcomes and neurodevelopmental abnormalities among offspring. Its prevalence in the United States and Europe is 12%-25%. This study examined the relationship between prenatal nicotine exposure (cotinine level) in archived maternal sera and schizophrenia in offspring from a national birth cohort.

METHOD

The authors conducted a population-based nested case-control study of all live births in Finland from 1983 to 1998. Cases of schizophrenia in offspring (N=977) were identified from a national registry and matched 1:1 to controls on date of birth, sex, and residence. Maternal serum cotinine levels were prospectively measured, using quantitative immunoassay, from early- to mid-gestation serum specimens archived in a national biobank.

RESULTS

A higher maternal cotinine level, measured as a continuous variable, was associated with an increased odds of schizophrenia (odds ratio=3.41, 95% confidence interval, 1.86-6.24). Categorically defined heavy maternal nicotine exposure was related to a 38% increased odds of schizophrenia. These findings were not accounted for by maternal age, maternal or parental psychiatric disorders, socioeconomic status, and other covariates. There was no clear evidence that weight for gestational age mediated the associations.

CONCLUSIONS

To the authors' knowledge, this is the first study of the relationship between a maternal smoking biomarker and schizophrenia. It provides the most definitive evidence to date that smoking during pregnancy is associated with schizophrenia. If replicated, these findings suggest that preventing smoking during pregnancy may decrease the incidence of schizophrenia.

Estimation for diffusion processes under misspecified models

The asymptotic behavior of the maximum likelihood estimator of a parameter in the drift term of a stationary ergodic diffusion process is studied under conditions in which the true drift function and true noise function do not coincide with those specified by the parametric model.

The Development of the Sexual Self-Concept Inventory for Early Adolescent Girls

The Sexual Self-Concept Inventory (SSCI) was developed to assess sexual self-concept in an ethnically diverse sample of urban early adolescent girls. Three scales (Sexual Arousability, Sexual Agency, and Negative Sexual Affect) were shown to be distinct and reliable dimensions of girls' sexual self-concepts. Validity was established through comparisons with established instruments. Sexual Arousability and Sexual Agency were associated with positive sexual self-esteem, positive future orientation toward sex, intentions to engage in intercourse, and lower levels of sexual experience. Negative Sexual Affect was associated with stronger abstinence attitudes and lack of intentions or orientation toward sex in the near future. The results indicate that the SSCI constitutes a valid means of assessing early adolescent girls' views of their sexuality and sexual behavior and may be of use in studies of health and risk-related decision making.

Hypothyroxinemia During Gestation and Offspring Schizophrenia in a National Birth Cohort

BACKGROUND

Evidence from animal and human studies indicates that thyroid hormone deficiency during early gestation alters brain development. As schizophrenia is associated with prenatal brain insults and premorbid cognitive deficits, we tested the a priori hypothesis that serologically defined maternal thyroid deficiency during early gestation to mid-gestation is associated with schizophrenia in offspring.

METHODS

The investigation is based on the Finnish Prenatal Study of Schizophrenia, a nested case-control study that included archived maternal sera from virtually all pregnancies since 1983 (N = >1 million). We identified all offspring in the cohort with a diagnosis of schizophrenia based on the national inpatient and outpatient register and matched them on sex, date of birth, and residence in Finland at time of onset of the case to comparison subjects (1:1) from the cohort. Maternal sera of 1010 case-control pairs were assessed for free thyroxine, and sera of 948 case-control pairs were assessed for thyroid-stimulating hormone.

RESULTS

Maternal hypothyroxinemia (free thyroxine ≤10th percentile, normal thyroid-stimulating hormone) was associated with an increased odds of schizophrenia (odds ratio = 1.75, 95% confidence interval = 1.22-2.50, p = .002). When adjusted for maternal psychiatric history, province of birth, and maternal smoking during pregnancy, the association remained significant (odds ratio = 1.70, 95% confidence interval = 1.13-2.55, p = .010).

CONCLUSIONS

In a large, national birth cohort, prospectively documented hypothyroxinemia during early gestation to mid-gestation was associated with increased odds of schizophrenia in offspring. This information can inform translational studies of maternal hypothyroxinemia examining molecular and cellular deviations relevant to schizophrenia.

Gestational Exposure to Selective Serotonin Reuptake Inhibitors and Offspring Psychiatric Disorders: A National Register-Based Study

OBJECTIVE

To investigate the impact of gestational exposure to selective serotonin reuptake inhibitors (SSRIs) on offspring neurodevelopment.

METHOD

This is a cohort study using national register data in Finland between the years 1996 and 2010. Pregnant women and their offspring were categorized into 4 groups: SSRI exposed (n = 15,729); exposed to psychiatric disorder, no antidepressants (n = 9,651); exposed to SSRIs only before pregnancy (n = 7,980); and unexposed to antidepressants and psychiatric disorders (n = 31,394). We investigated the cumulative incidence of offspring diagnoses of depression, anxiety, autism spectrum disorder (ASD), and attention-deficit/hyperactivity disorder (ADHD) for the 4 groups from birth to 14 years, adjusting for confounders.

RESULTS

The cumulative incidence of depression among offspring exposed prenatally to SSRIs was 8.2% (95% CI = 3.1-13.3%) by age 14.9 years, compared with 1.9% (95% CI = 0.9-2.9%) in the psychiatric disorder, no medication group (adjusted hazard ratio [HR] = 1.78; 95% CI = 1.12-2.82; p = .02) and to 2.8% (95% CI = 1.4-4.3%) in the SSRI discontinued group (HR = 1.84; 95% CI = 1.14-2.97; p = .01). Rates of anxiety, ASD, and ADHD diagnoses were comparable to rates in offspring of mothers with a psychiatric disorder but no medication during pregnancy. Comparing SSRI exposed to unexposed individuals, the HRs were significantly elevated for each outcome.

CONCLUSION

Prenatal SSRI exposure was associated with increased rates of depression diagnoses in early adolescence but not with ASD or ADHD. Until confirmed, these findings must be balanced against the substantial adverse consequences of untreated maternal depression.

An adaptive resampling test for detecting the presence of significant predictors

This paper investigates marginal screening for detecting the presence of significant predictors in high-dimensional regression. Screening large numbers of predictors is a challenging problem due to the non-standard limiting behavior of post-model-selected estimators. There is a common misconception that the oracle property for such estimators is a panacea, but the oracle property only holds away from the null hypothesis of interest in marginal screening. To address this difficulty, we propose an adaptive resampling test (ART). Our approach provides an alternative to the popular (yet conservative) Bonferroni method of controlling familywise error rates. ART is adaptive in the sense that thresholding is used to decide whether the centered percentile bootstrap applies, and otherwise adapts to the non-standard asymptotics in the tightest way possible. The performance of the approach is evaluated using a simulation study and applied to gene expression data and HIV drug resistance data.

Empirical likelihood based tests for stochastic ordering under right censorship

This paper develops an empirical likelihood approach to testing for stochastic ordering between two univariate distributions under right censorship. The proposed test is based on a maximally selected local empirical likelihood statistic. The asymptotic null distribution is expressed in terms of a Brownian bridge. The new procedure is shown via a simulation study to have superior power to the log-rank and weighted Kaplan-Meier tests under crossing hazard alternatives. The approach is illustrated using data from a randomized clinical trial involving the treatment of severe alcoholic hepatitis.

Pregnancy Complications Following Prenatal Exposure to SSRIs or Maternal Psychiatric Disorders: Results From Population-Based National Register Data

OBJECTIVE

Using national register data, the authors examined the relationship between prenatal selective serotonin reuptake inhibitor (SSRI) treatment and pregnancy complications, accounting for psychiatric diagnoses related to SSRI use.

METHOD

This was a population-based prospective birth cohort study using national register data. The sampling frame included 845,345 offspring, representing all singleton live births in Finland between 1996 and 2010. Pregnancies were classified as exposed to SSRIs (N=15,729), unexposed to SSRIs but with psychiatric diagnoses (N=9,652), and unexposed to medications and psychiatric diagnoses (N=31,394). Pregnancy outcomes in SSRI users were compared with those in the unexposed groups.

RESULTS

Offspring of mothers who received SSRI prescriptions during pregnancy had a lower risk for late preterm birth (odds ratio=0.84, 95% CI=0.74-0.96), for very preterm birth (odds ratio=0.52, 95% CI=0.37-0.74), and for cesarean section (odds ratio=0.70, 95% CI=0.66-0.75) compared with offspring of mothers unexposed to medications but with psychiatric disorders. In contrast, in SSRI-treated mothers, the risk was higher for offspring neonatal complications, including low Apgar score (odds ratio=1.68, 95% CI=1.34-2.12) and monitoring in a neonatal care unit (odds ratio=1.24, 95% CI=1.14-1.35). Compared with offspring of unexposed mothers, offspring of SSRI-treated mothers and mothers unexposed to medications but with psychiatric disorders were both at increased risk of many adverse pregnancy outcomes, including cesarean section and need for monitoring in a neonatal care unit.

CONCLUSIONS

In a large national birth cohort, treatment of maternal psychiatric disorders with SSRIs during pregnancy was related to a lower risk of preterm birth and cesarean section but a higher risk of neonatal maladaptation. The findings provide novel evidence for a protective role of SSRIs on some deleterious reproductive outcomes, possibly by reducing maternal depressive symptoms. The divergent findings suggest that clinical decisions on SSRI use during pregnancy should be individualized, taking into account the mother's psychiatric and reproductive history.

Optimal design strategies for sibling studies with binary exposures

Sibling studies have become increasingly popular because they provide better control over confounding by unmeasured family-level risk factors than can be obtained in standard cohort studies. However, little attention has been devoted to the development of efficient design strategies for sibling studies in terms of optimizing power. We here address this issue in commonly encountered types of sibling studies, allowing for continuous and binary outcomes and varying numbers of exposed and unexposed siblings. For continuous outcomes, we show that in families with sibling pairs, optimal study power is obtained by recruiting discordant (exposed-control) pairs of siblings. More generally, balancing the exposure status within each family as evenly as possible is shown to be optimal. For binary outcomes, we elucidate how the optimal strategy depends on the variation of the binary response; as the within-family correlation increases, the optimal strategy tends toward only recruiting discordant sibling pairs (as in the case of continuous outcomes). R code for obtaining the optimal strategies is included.

Autism with intellectual disability related to dynamics of head circumference growth during early infancy

BACKGROUND

It is not yet definitively known whether dynamic features of head circumference growth are associated with autism. To address this issue, we carried out a nested matched case-control study using data from national well baby clinics in Finland; autism cases were identified from the Finnish Hospital and Outpatient Discharge Registry.

METHODS

A nonparametric Bayesian method was used to construct growth velocity trajectories between birth and 2 years of age in autism cases and matched control subjects (n = 468 in main analyses, 1:1 matched control subjects). Estimates of odds ratios for autism risk in relation to the growth velocities were obtained using conditional logistic regression.

RESULTS

Growth velocity of head circumference at 3 months of age, adjusting for gestational age at birth and maternal age, is significantly associated with autism (p = .014); the finding was observed in subjects with comorbid intellectual disability (ID) (p = .025) but not in those without ID (p = .15). Height growth velocity among subjects with autism and without ID is significantly associated with autism at 6 months (p = .007), and weight growth velocity at 18 months without ID (p = .02) and 24 months without ID (p = .042) and with ID (p = .037).

CONCLUSIONS

Acceleration in head circumference growth is associated with autism with comorbid ID at 3 months but not subsequently. This association is unrelated to acceleration in height and weight, which are not strongly associated with autism until after 6 months.

Central limit theorems under special relativity

Several relativistic extensions of the Maxwell-Boltzmann distribution have been proposed, but they do not explain observed lognormal tail-behavior in the flux distribution of various astrophysical sources. Motivated by this question, extensions of classical central limit theorems are developed under the conditions of special relativity. The results are related to CLTs on locally compact Lie groups developed by Wehn, Stroock and Varadhan, but in this special case the asymptotic distribution has an explicit form that is readily seen to exhibit lognormal tail behavior.

Reduction in incidence of hospitalizations for psychotic episodes through early identification and intervention

OBJECTIVE

This study examined whether the incidence of hospitalization for psychosis was reduced by a communitywide system of early identification and intervention to prevent onset of psychosis.

METHODS

The Portland Identification and Early Referral program (PIER) was initiated in 2001. Youths and young adults ages 12-35 were identified by professionals in a wide variety of educational, health, and mental health settings. PIER program staff assessed, confirmed risk of psychosis, and provided treatment for 24 months to eligible and consenting young people (N=148). The monthly rate of first hospital admission for psychosis was the outcome measure for efficacy of identification and intervention. Admission rates before and after the program began accepting referrals were compared, both in the experimental area (Greater Portland) and in aggregated urban areas of Maine (control areas). Autoregressive integrated moving-average (ARIMA) models were used to assess the effect.

RESULTS

On the basis of ARIMA models, the rate of first hospital admission for psychosis decreased significantly by 26% (95% confidence interval [CI]=-64% to -11%) in the Greater Portland area. The rate increased by 8% (CI=-5% to 36%) in the control areas. Taking into account the increase in the control areas, the actual percentage reduction in Greater Portland during the intervention period was 34% (26% plus 8%). The reduction in admissions was largest for individuals with nonaffective nonschizophrenic psychosis.

CONCLUSIONS

PIER has demonstrated that populationwide early identification is feasible. Preventive intervention can reduce rates of initial hospitalizations for psychosis in a midsized city.

Elevated maternal C-reactive protein and increased risk of schizophrenia in a national birth cohort

OBJECTIVE

The objective of the present study was to investigate an association between early gestational C-reactive protein, an established inflammatory biomarker, prospectively assayed in maternal sera, and schizophrenia in a large, national birth cohort with an extensive serum biobank.

METHOD

A nested case-control design from the Finnish Prenatal Study of Schizophrenia cohort was utilized. A total of 777 schizophrenia cases (schizophrenia, N=630; schizoaffective disorder, N=147) with maternal sera available for C-reactive protein testing were identified and matched to 777 control subjects in the analysis. Maternal C-reactive protein levels were assessed using a latex immunoassay from archived maternal serum specimens.

RESULTS

Increasing maternal C-reactive protein levels, classified as a continuous variable, were significantly associated with schizophrenia in offspring (adjusted odds ratio=1.31, 95% confidence interval=1.10-1.56). This finding remained significant after adjusting for potential confounders, including maternal and parental history of psychiatric disorders, twin/singleton birth, urbanicity, province of birth, and maternal socioeconomic status.

CONCLUSIONS

This finding provides the most robust evidence to date that maternal inflammation may play a significant role in schizophrenia, with possible implications for identifying preventive strategies and pathogenic mechanisms in schizophrenia and other neurodevelopmental disorders.

Estimation of treatment policies based on functional predictors

Biosignatures such as brain scans, mass spectrometry, or gene expression profiles might one day be used to guide treatment selection and improve outcomes. This article develops a way of estimating optimal treatment policies based on data from randomized clinical trials by interpreting patient biosignatures as functional predictors. A flexible functional regression model is used to represent the treatment effect and construct the estimated policy. The effectiveness of the estimated policy is assessed by furnishing prediction intervals for the mean outcome when all patients follow the policy. The validity of these prediction intervals is established under mild regularity conditions on the functional regression model. The performance of the proposed approach is evaluated in numerical studies.

Finnish Prenatal Study of Bipolar Disorders (FIPS-B): overview, design and description of the sample

BACKGROUND

Bipolar disorders (BPD) are chronic mental illnesses, the development of which involves genetic factors and environmental influences.

AIMS

The aim of this paper is to provide an overall description of the Finnish Prenatal Study of Bipolar Disorders (FIPS-B), including the study design, national registers and linkage of the registers.

METHODS

FIPS-B is a population-based prenatal epidemiological study of BPD with a nested case-control study design using several national registers. The registers used are: the Finnish Medical Birth Register (FMBR), the Finnish Hospital Discharge Register (FHDR), the Population Central Register and the Finnish Maternity Cohort (FMC), which are linked using the unique personal identity code (PIC). FIPS-B includes all children born from January 1, 1983 to December 31, 1998 and diagnosed with BPD in Finland by December 31, 2008.

RESULTS

The total number of cases included in the FIPS-B is 1887. The age at first diagnosis ranged from 4 to 25 years. Half (50.4%) of the cases utilized only outpatient services, 12.7% only inpatient services and the rest (36.9%) utilized both services. Offspring of mothers with the lowest educational level had an increased odds of BPD (OR = 1.46, 95% CI 1.13-1.88). The cumulative incidence of BPD in the population aged 25 years or younger was 11.6/10,000 in 2008.

CONCLUSIONS

FIPS-B has all the strengths of a register-based prenatal epidemiological study, along with the availability of maternal biomarkers, enabling it to examine several prenatal, perinatal and familial risk factors for BPD.

Circulating pro-surfactant protein B as a risk biomarker for lung cancer

BACKGROUND

Our prior studies of lung cancer suggested that a novel biomarker (pro-surfactant protein B or pro-SFTPB) might serve as a predictive marker for this disease. We aimed to determine the potential use of pro-SFTPB for distinguishing lung cancer cases from matched controls as a risk marker.

METHODS

Study subjects were drawn from the longitudinal Physicians' Health Study (PHS). Cases (n = 188) included individuals who were cancer-free at study enrollment but developed lung cancer during follow-up. Controls (n = 337) were subjects who did not develop lung cancer. Cases and controls were matched on date of study enrollment, age at enrollment, and smoking status and amount. Baseline plasma samples drawn at enrollment were analyzed for pro-SFTPB using ELISA to detect differences in protein expression levels for cases and controls.

RESULTS

Pro-SFTPB nondetectable status was significantly associated with lung cancer risk [OR = 5.88; 95% confidence interval (CI) 1.24-27.48]. Among subjects with detectable levels of the protein, increasing plasma concentration of pro-SFTPB was associated with higher lung cancer risk (OR = 1.41 per unit increase in log pro-SFTPB; 95% CI 1.08-1.84).

CONCLUSION

These results suggest a nonlinear, J-shaped association between plasma pro-SFTPB levels and lung cancer risk, with both nondetectable and higher levels of the marker being associated with lung cancer.

IMPACT

These results show promise of a risk marker that could contribute to predicting risk for lung cancer development and to narrowing the high-risk population for low-dose computed tomography screening.

Maternal serum persistent organic pollutants in the Finnish Prenatal Study of Autism: A pilot study

Recent research emphasizes the contribution of environmental as well as genetic factors to the etiology of autism but studies testing associations between chemical exposures and autism have been limited. Prenatal exposure to persistent organic pollutants (POPs) has previously been associated with decrements in cognitive and developmental performance. We conducted a pilot study in the Finnish Prenatal Study of Autism (FiPS-A). Seventy-five cases with autism and 75 controls matched on sex, birth year, urbanization and maternal age were sampled from first-born children in the Finnish Maternity Cohort, which includes over 1million births. The study sample included births occurring from 1991 to 2000. Subjects were followed up for autism through 2007. DDT, DDE, PCB-118, PCB-138, PCB-153, PCB-156, PCB-170, PCB-180, hexachlorobenzene, and BDE-47 were measured in archived maternal serum samples taken during pregnancy using gas chromatography-high resolution mass spectrometry. Correlations between pollutant measures were assessed and mechanistically-related weighting schemes for summarizing PCB levels were compared. Case and control differences were assessed using graphical and statistical methods. All analytes, with the exception of DDT and BDE-47, were detected above the limit of quantification in all samples. The correlation between levels of individual PCB congeners and weighted summary measures was high (0.71-1.00). Paired t-tests revealed no significant differences between cases and controls for log-transformed mean values of any analyte; however, in an adjusted model the odds ratios for autism were 1.91 (p=0.29) and 1.79 (p=0.36) respectively, for subjects with total PCBs and DDE above the 90th percentile of control values. Levels of prenatal PCB exposure in FIPS-A were similar to the levels which previously correlated with poorer neurodevelopmental measures in other populations. Further study in a larger sample will be required to fully determine whether exposure to high POP levels is associated with autism diagnosis in the population.

Severity and persistence of asthma and mental health: a birth cohort study

BACKGROUND

The goal of the current study was to investigate asthma and mental health among youth in the community, and to consider the role of asthma severity and persistence in this link. Method Data were drawn from the Raine Study, a population-based birth cohort study in Western Australia. Logistic regression models and generalized estimating equations were used to examine the relationship between asthma at age 5 years and the range of internalizing and externalizing mental health problems at ages 5-17 years. Analyses were stratified by asthma severity and persistence, and adjusted for a range of potential confounders.

RESULTS

More severe and persistent asthma at age 5 was associated with significantly increased odds of affective, anxiety, somatic, oppositional defiant and conduct problems at ages 5-17. Mild asthma and remitted asthma were not associated with heightened vulnerability to mental disorders.

CONCLUSIONS

Our results suggest that youth with symptomatic asthma are more likely to suffer from a wide range of mental health problems, and that the likelihood of mental health problems appears to increase as a function of asthma severity. Youth with poorly controlled and/or more severe and persistent asthma may be considered a vulnerable group who might benefit from mental health screening in clinical, school and community settings.

Birth weight and neurocognition in schizophrenia spectrum disorders

Low birth weight is associated with both schizophrenia and neurocognitive impairment. Yet, to our knowledge, no previous study has examined the relationship between lower birth weight and neurocognitive deficits in schizophrenia spectrum disorders (SSD). In this preliminary study, we investigated the relationship using a broad neuropsychological battery in cases with SSD and matched control subjects. The sample consisted of all subjects in the Developmental Insult and Brain Anomaly in Schizophrenia study, a nested case-control investigation developed from a large birth cohort, which followed subjects longitudinally. Case ascertainment was based on computerized record linkages between the birth cohort members and the Kaiser Permanente Medical Care Plan, and all diagnoses were confirmed by consensus diagnosis following the Diagnostic Interview for Genetic Studies. Lower birth weight was associated with impairment in executive function, working memory, generalized intellectual function, and neuromotor function in cases with SSD but not in control subjects. No deficits were observed in verbal memory for either group. These results support the hypothesis that lower birth weight plays a role in neuropsychological disruptions in SSD and that the antecedents of lower birth weight may have a greater impact on these disruptions in SSD than in controls. These data may facilitate a better understanding of the etiopathogenesis of the cognitive underpinnings of SSD.

Recovering gradients from sparsely observed functional data

The recovery of gradients of sparsely observed functional data is a challenging ill-posed inverse problem. Given observations of smooth curves (e.g., growth curves) at isolated time points, the aim is to provide estimates of the underlying gradients (or growth velocities). To address this problem, we develop a Bayesian inversion approach that models the gradient in the gaps between the observation times by a tied-down Brownian motion, conditionally on its values at the observation times. The posterior mean and covariance kernel of the growth velocities are then found to have explicit and computationally tractable representations in terms of quadratic splines. The hyperparameters in the prior are specified via nonparametric empirical Bayes, with the prior precision matrix at the observation times estimated by constrained ℓ₁ minimization. The infinitessimal variance of the Brownian motion prior is selected by cross-validation. The approach is illustrated using both simulated and real data examples.

Power and Sample Size Calculations for Generalized Estimating Equations via Local Asymptotics

We consider the problem of calculating power and sample size for tests based on generalized estimating equations (GEE), that arise in studies involving clustered or correlated data (e.g., longitudinal studies and sibling studies). Previous approaches approximate the power of such tests using the asymptotic behavior of the test statistics under fixed alternatives. We develop a more accurate approach in which the asymptotic behavior is studied under a sequence of local alternatives that converge to the null hypothesis at root-m rate, where m is the number of clusters. Based on this approach, explicit sample size formulae are derived for Wald and quasi-score test statistics in a variety of GEE settings. Simulation results show that in the important special case of logistic regression with exchangeable correlation structure, previous approaches can inflate the projected sample size (to obtain nominal 90% power using the Wald statistic) by over 10%, whereas the proposed approach provides an accuracy of around 2%.