Profiling heteroscedasticity in linear regression models

Diagnostics for heteroscedasticity in linear regression models have been intensively investigated in the literature. However, limited attention has been paid on how to identify covariates associated with heteroscedastic error variances. This problem is critical in correctly modelling the variance structure in weighted least squares estimation, which leads to improved estimation efficiency. We propose covariate‐specific statistics based on information ratios formed as comparisons between the model‐based and sandwich variance estimators. A two‐step diagnostic procedure is established, first to detect heteroscedasticity in error variances, and then to identify covariates the error variance structure might depend on. This proposed method is generalized to accommodate practical complications, such as when covariates associated with the heteroscedastic variances might not be associated with the mean structure of the response variable, or when strong correlation is present amongst covariates. The performance of the proposed method is assessed via a simulation study and is illustrated through a data analysis in which we show the importance of correct identification of covariates associated with the variance structure in estimation and inference. The Canadian Journal of Statistics 43: 358–377; 2015 © 2015 Statistical Society of CanadaRésuméLes outils de diagnostic pour l'hétéroscédasticité dans les modèles de régression linéaire sont largement étudiés dans la littérature. Toutefois, l'identification des covariables associées aux variances hétéroscédastiques n'a suscité que peu d'intérêt. Ce problème joue pourtant un rôle clé pour l'estimation par les moindres carrés pondérés, puisque la modélisation correcte de la structure de variance accroî t l'efficacité de l'estimation. Les auteurs proposent des statistiques spécifiques aux covariables fondées sur un ratio d'information comparant l'estimateur de la variance basé sur le modèle à l'estimateur sandwich de la variance. Ils développent une procédure diagnostique en deux étapes, détectant d'abord l'hétéroscédasticité et identifiant ensuite les covariables dont peut dépendre la structure de variance. Ils généralisent la méthode proposée afin d'accommoder des complications pratiques telles que l'absence de lien entre la structure de la moyenne et une covariable associée avec l'hétéroscédasticité, ou la forte corrélation des covariables. Les auteurs évaluent la performance de la méthode proposée à l'aide d'une étude de simulation et l'illustrent en analysant un jeu de données montrant l'importance d'identifier correctement les covariables associées avec la structure de variance pour l'estimation et l'inférence. La revue canadienne de statistique xx: 1–20; 2015 © 2015 Société statistique du CanadaPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/113149/1/cjs11252.pd

Calibration and quality assurance for rounded leaf‐end MLC systems

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134970/1/mp3517.pd

Disciplinary Segregation’s Effects on Inmate Behavior: Institutional and Community Outcomes

Disciplinary segregation (DS) is practiced in a variety of correctional settings and a growing body of research explores its subsequent effects among offenders. The present study contributes to this literature by analyzing the impact of short-term DS on violent infractions and community recidivism among a sample of inmates in Washington State. We assessed the impact of DS on these outcomes from deterrence and stain theory perspectives while controlling for social support variables such as visitations and correctional programming. Mentally ill offenders were excluded, as their abilities to make rational choices may be inconsistent with deterrence theory. Results show DS does not significantly affect post-DS infractions. Social supports significantly reduced inmates’ odds of violent infractions while incarcerated. Community models indicate no substantive differences between the DS and non-DS groups on post-prison convictions 3 years after release. Overall, DS exhibited limited effects on offenders’ institutional or community outcomes

Macrocerebellum: Neuroimaging and Clinical Features of a Newly Recognized Condition

Other than hamartomatous enlargement of the cerebellum as in Lhermitte-Duclos syndrome, diffuse enlargement of the cerebellum is not clearly described. We report four patients (ages 9 months to 2 years) with diffusely enlarged cerebelli as identified by measurement of the cerebellum and comparison to age appropriate normal values. The cerebellar measurements were determined in absolute numbers and expressed as ratios of cerebellum to whole brain and supratentorial brain. The clinical features of these four children (3 boys, 1 girl) consistently include global developmental delay, tone abnormalities, preserved reflexes, delayed or abnormal maturation of the visual system (oculomotor apraxia), and deficient or delayed myelination of cerebral white matter. The etiology of the macrocerebellum is unknown but we propose that the cerebellum is responding to the elaboration of growth factors intended to augment the slow development of cerebral structures. Regardless of the etiology, the finding of a macrocerebellum appears to allow the clinician to predict the clinical features of the patient and probably represents a marker for disturbed cerebral development. (J Child Neurol 1997;12:365-368).Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Initiating technological and pedagogical shifts in low achieving urban minority classrooms

This study explored the introduction of multi-modal teaching strategies alongside technology implementation in high poverty schools. Teachers were provided with scientific tools, simulations, and teaching stations and provided with training and opportunities to practice teaching strategies developed in conjunction with special education and literacy experts. Teacher interviews, classroom observations, and student focus groups comprised the bulk of the sited data supplementing the student achievement scores and pre and post content tests administered for each unit. Findings suggested not all teachers incorporated multi-modal strategies into lessons incorporating technology and that lower achieving students interpreted lessons quite differently than their teachers in these contexts. Implications for ways technology implementations may explicate emerging literacies are discussed

Understanding Offender Needs Over Forms of Isolation Using a Repeated Measures Design

A number of studies find that solitary confinement is associated with mental impairment. Yet, confinement dosage and which individual and exogenous variables lead to mental impairment have received less attention. This study of 2 years of data on disciplinary segregation male inmates employs a repeated measures design to examine how isolation affects mental health and psychological needs. The findings indicate that the duration of disciplinary segregation and incarceration, incidence of homelessness, and other individual-level factors had deleterious effects on mental health and psychological needs. Vocational programming and a high school education were found to be protective factors for psychological needs

Right orbitofrontal corticolimbic and left corticocortical white matter connectivity differentiate bipolar and unipolar depression

Objectives - The absence of pathophysiologically relevant diagnostic markers of bipolar disorder (BD) leads to its frequent misdiagnosis as unipolar depression (UD). We aimed to determine whether whole brain white matter connectivity differentiated BD from UD depression. Methods - We employed a three-way analysis of covariance, covarying for age, to examine whole brain fractional anisotropy (FA), and corresponding longitudinal and radial diffusivity, in currently depressed adults: 15 with BD-type I (mean age 36.3 years, SD 12.0 years), 16 with recurrent UD (mean age 32.3 years, SD 10.0 years), and 24 healthy control adults (HC) (mean age 29.5 years, SD 9.43 years). Depressed groups did not differ in depression severity, age of illness onset, and illness duration. Results - There was a main effect of group in left superior and inferior longitudinal fasciculi (SLF and ILF) (all F = 9.8; p = .05, corrected). Whole brain post hoc analyses (all t = 4.2; p = .05, corrected) revealed decreased FA in left SLF in BD, versus UD adults in inferior temporal cortex and, versus HC, in primary sensory cortex (associated with increased radial and decreased longitudinal diffusivity, respectively); and decreased FA in left ILF in UD adults versus HC. A main effect of group in right uncinate fasciculus (in orbitofrontal cortex) just failed to meet significance in all participants but was present in women. Post hoc analyses revealed decreased right uncinate fasciculus FA in all and in women, BD versus HC. Conclusions - White matter FA in left occipitotemporal and primary sensory regions supporting visuospatial and sensory processing differentiates BD from UD depression. Abnormally reduced FA in right fronto-temporal regions supporting mood regulation, might underlie predisposition to depression in BD. These measures might help differentiate pathophysiologic processes of BD versus UD depression

Hashimoto's thyroiditis revisited: The association with thyroid cancer remains obscure

Hashimoto's thyroiditis (HT) is an autoimmune disease of the thyroid associated with goiter and hypothyroidism. Although there exists a clear association between HT and lymphomas of the thyroid, the association between HT and thyroid cancer remains unclear. To evaluate this further, we retrospectively reviewed the pathology reports for all thyroidectomy specimens as well as the records of patients admitted to the University of Michigan Medical Center, Ann Arbor, Michigan, U.S.A., over a 10-yearperiod (1975–1985) with the diagnosis of HT or chronic lymphocytic thyroiditis (CLT). Eight hundred and nine pathologic diagnoses were recorded for 816 thyroidectomy specimens from 793 patients. Furthermore, 180 of 228 patient chart records were available for review. Only 128 patients satisfied our criteria for the diagnosis of HT. HT or CLT were diagnosed in 147 (18.2%) of 809 thyroid specimens. HT occurred concurrently with thyroid cancer in 24% of all cases of HT, whereas, HT occurred concurrently with benign thyroid disease in 71% of all cases of HT in all thyroid specimens. Furthermore, HT was associated with 43 (22%) of 195 cases of thyroid cancer. There were 111 (87%) women and 17 (13%) men of 128 patients whose charts were reviewed. The mean age was 49±14 years. Ninety-eight (77%) of the patients presented with goiters and 57 (45%) presented with dominant thyroid masses, 38 (67%) of which were solitary nodules. One patient (0.8%) presented with a recurrent laryngeal nerve palsy (RLNP) and 12 (9%) presented with tracheal compression. Only 29 (38.2%) of 76 patients measured had positive antithyroglobulin (ATG) titers, whereas 65 (87%) of 75 patients measured had positive antimicrosomal (AM) titers. Seventy (55%) patients were evaluated with either a technetium or 131 I thyroid scan. There was a heterogeneous pattern to the scan in 75% of these patients. Niney-one (71%) patients were initially treated with thyroid suppression. However, 27 (21%) required thyroidectomy for initial management. Ultimately, 60% required thyroidectomy and 37% required none. The major indication for surgical intervention was the presence of a dominant mass in 40 (52%) of 77 patients. Only 17 (13%) patients were found to have thyroid cancer concomitant with HT and 3(2%) had lymphoma with HT. The incidence of minimal (occult) cancer in a study of 100 consecutive autopsies at this institution was 13%. We believe that these data suggest that the association of HT with thyroid cancer is relative, at best. It will be necessary to prospectively follow both a large group of patients with HT and a control group of patients without HT for the incidence of thyroid cancer in each before this issue can be appropriately addressed. La thyroïdite d'Hashimoto (TH) est une maladie autoimmune de la thyroïde qui provoque goitre et hyperthyroïdisme. Bien que l'association entre TH et lymphome de la thyroïde soit bien établie, celle entre TH et cancer de la thyroïde reste confuse. Pour essayer de mieux élucider cette question, les auteurs ont revu rétrospectivement les comptes rendus d'histologie de toutes les pièces de thyroïdectomie, et les dossiers de tous les patients admis pendant la période 1975–1985 avec le diagnostic de TH ou de thyroïdite lymphocytique chronique (TLC). Il y avait 809 diagnostics enrégistrés pour 816 pièces de thyroïdectomie provenant de 793 patients. En outre, 180 dossiers sur 228 étaient exploitables. Cent-vingt-huit patients seulement remplissaient les conditions diagnostiques de TH. TH ou TLC étaient diagnostiquées dans 147 (18.2%) pièces sur 809. La TH était associée avec un cancer dans 24% de tous les cas de TH, alors que la TH était associée à une maladie bénigne de la thyroïde dans 71% des cas de TH. La TH était présente dans 43 (22%) sur 195 des cas de cancer de la thyroïde. Il y avait 111 (87%) femmes et 17 hommes (13%). L'âge moyen était de 49±14 ans. Quatre-vingt-huit patients (77%) avaient un goitre et 57 (45%) une masse, 38 (67%) étant un nodule solitaire. Un patient (0.8%) avait d'emblée une paralysie récurrentielle et 12 (9%) avaient une compression trachéale. Vingt-neuf (38.2%) patients seulement sur 76 avaient des anticorps antithyroglobuline thyroïdiens, et 67 (87%) des 75 patients avaient des anticorps antimicrosomiaux. Soixante-dix patients (55%) ont eu une scintigraphie au technetium ou à l'I 131: la thyroïde était hétérogène pour 75% d'entre eux. Quatre-vingt un patients (71%) ont eu une hormonothérapie suppressive en premier, alors que 27 (21%) ont eu une thyroïdectomie première. Ultérieurement, 60% des patients ont été thyroïdectomisés. L'indication principale de la chirurgie était la présence d'une masse, trouvée chez 40 (52%) des 77 patients. Seuls 17 (13%) patients avec une TH avaient un cancer simultané de la thyroïde; 3 (2%) avaient un lymphome associé à une TH. La fréquence de cancer occulte dans une étude de 100 autopsies consécutives dans notre établissement était de 13%. Nous pensons que ces résultats suggèrent que l'association TH cancer de la thyroïde n'est que fortuite. Il est nécessaire de suivre prospectivement un grand nombre de patients, divisés en 2 groupes, les uns avec TH, les autres sans, pour déterminer avec précision l'incidence de cancer dans chaque groupe avant de résoudre ce problème. La tiroiditis de Hashimoto (TH) es una enfermedad autoinmune de la tiroides, asociada con bocio e hipotiroidismo. Aunque existe una clara relación entre TH y linfomas de la tiroides, la relación entre TH y cáncer tiroideo no aparece clara. Con el fín de evaluar este asunto, hemos revisado en forma retrospectiva tanto los informes de patología de todos los especímenes de tiroidectomía, así como las historias clínicas de los pacientes admitidos al Centro Médico de la Universidad de Michigan, Ann Arbor, Michigan, con el diagnóstico de TH o de tiroiditis linfocítica crónica (TLC) en un período de 10 años (1975–1985). Se registraron 809 diagnósticos patológicos de 816 especímenes de tiroidectomía en 793 pacientes. Además, se dispuso de 180 de 228 historias clínicas para revisión. Sólo 128 pacientes satisficieron nuestros criterios para el diagnóstico de TH. TH o TLC fueron diagnosticadas en 147 (18.2%) de 809 de los Especímenes tiroideos. La TH ocurrió en forma concurrente con el cáncer tiroideo en 24% de todos los casos de TH, en tanto que la TH ocurrió en forma concurrente con enfermedad benigna de la tiroides en 71% de la totalidad de los casos de TH en todos los especímenes tiroideos. Se encontraron 111 (87%) mujeres y 17 (13%) hombres de 128 pacientes cuyas historias clínicas fueron revisadas: la edad promedio fue 49±14 años. Noventa y ocho (77%) de los pacientes presentaban bocio y 57 (45%) presentaban masas tiroideas dominantes, de las cuales 38 (67%) eran nódulos solitarios. Un paciente (0.8%) se presentó con parálisis del nervio recurrente laríngeo y 12 (9%) con compresión traqueal. Sólo 29 (38.2%) de 76 pacientes investigados tenían títulos positivos de ATG, mientras 65 (87%) de 75 tenían títulos AM positivos. Setenta (55%) fueron evaluados mediante escanografía con tecnecio o con 131 I; se observó un patrón heterogéneo en la gamagrafía en 75% de ellos. Noventa y uno (71%) fueron tratados inicialmente con supresión tiroidea. Sin embargo, 27 (21%) requirieron tiroidectomía en su manejo inicial. Al final 60% requirieron tiroidectomía y 37% no la requirieron. La indicación mayor para intervención quirúrgica fue la presencia de una masa dominante en 40 (52%) de 77 pacientes. Sólo 17 (13%) pacientes exhibieron cáncer tiroideo concomitante con TH y 3 (2%) presentaron linfoma con TH. La incidencia de cáncer mínimo (oculto) en un estudio de 100 autopsias consecutivas en nuestra institución fue 13%. Consideramos que estos datos sugieren que la relación entre TH y cáncer tiroideo es apenas relativa, en el mejor de los casos. Será necesario hacer el seguimiento prospectivo de un grupo grande de pacientes con TH y de un grupo control sin TH para detectar la incidencia de cáncer tiroideo en cada grupo para poder enfocar en forma apropiada este asunto.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41280/1/268_2005_Article_BF01655435.pd