Jeffrey S. Buzas

Mortality and Neonatal Morbidity Among Infants 501 to 1500 Grams From 2000 to 2009

OBJECTIVE: To identify changes in mortality and neonatal morbidities for infants with birth weight 501 to 1500 g born from 2000 to 2009. METHODS: There were 355 806 infants weighing 501 to 1500 g who were born in 2000–2009. Mortality during initial hospitalization and major neonatal morbidity in survivors (early and late infection, chronic lung disease, necrotizing enterocolitis, severe retinopathy of prematurity, severe intraventricular hemorrhage, and periventricular leukomalacia) were assessed by using data from 669 North American hospitals in the Vermont Oxford Network. RESULTS: From 2000 to 2009, mortality for infants weighing 501 to 1500 g decreased from 14.3% to 12.4% (difference, −1.9%; 95% confidence interval, −2.3% to −1.5%). Major morbidity in survivors decreased from 46.4% to 41.4% (difference, −4.9%; 95% confidence interval, −5.6% to −4.2%). In 2009, mortality ranged from 36.6% for infants 501 to 750 g to 3.5% for infants 1251 to 1500 g, whereas major morbidity in survivors ranged from 82.7% to 18.7%. In 2009, 49.2% of all very low birth weight infants and 89.2% of infants 501 to 750 g either died or survived with a major neonatal morbidity. CONCLUSIONS: Mortality and major neonatal morbidity in survivors decreased for infants with birth weight 501 to 1500 g between 2000 and 2009. However, at the end of the decade, a high proportion of these infants still either died or survived after experiencing ≥1 major neonatal morbidity known to be associated with both short- and long-term adverse consequences.

North Atlantic Deepwater Temperature Change During Late Pliocene and Late Quaternary Climatic Cycles

Variations in the ratio of magnesium to calcium (Mg/Ca) in fossil ostracodes from Deep Sea Drilling Project Site 607 in the deep North Atlantic show that the change in bottom water temperature during late Pliocene 41,000-year obliquity cycles averaged 1.5°C between 3.2 and 2.8 million years ago (Ma) and increased to 2.3°C between 2.8 and 2.3 Ma, coincidentally with the intensification of Northern Hemisphere glaciation. During the last two 100,000-year glacial-to-interglacial climatic cycles of the Quaternary, bottom water temperatures changed by 4.5°C. These results show that glacial deepwater cooling has intensified since 3.2 Ma, most likely as the result of progressively diminished deepwater production in the North Atlantic and of the greater influence of Antarctic bottom water in the North Atlantic during glacial periods. The ostracode Mg/Ca data also allow the direct determination of the temperature component of the benthic foraminiferal oxygen isotope record from Site 607, as well as derivation of a hypothetical sea-level curve for the late Pliocene and late Quaternary. The effects of dissolution on the Mg/Ca ratios of ostracode shells appear to have been minimal.

Comparing Scat Detection Dogs, Cameras, and Hair Snares for Surveying Carnivores

Abstract Carnivores typically require large areas of habitat, exist at low natural densities, and exhibit elusive behavior—characteristics that render them difficult to study. Noninvasive survey methods increasingly provide means to collect extensive data on carnivore occupancy, distribution, and abundance. During the summers of 2003–2004, we compared the abilities of scat detection dogs, remote cameras, and hair snares to detect black bears (Ursus americanus), fishers (Martes pennanti), and bobcats (Lynx rufus) at 168 sites throughout Vermont. All 3 methods detected black bears; neither fishers nor bobcats were detected by hair snares. Scat detection dogs yielded the highest raw detection rate and probability of detection (given presence) for each of the target species, as well as the greatest number of unique detections (i.e., occasions when only one method detected the target species). We estimated that the mean probability of detecting the target species during a single visit to a site with a detection dog was 0.87 for black bears, 0.84 for fishers, and 0.27 for bobcats. Although the cost of surveying with detection dogs was higher than that of remote cameras or hair snares, the efficiency of this method rendered it the most cost-effective survey method.

Weight Growth Velocity and Postnatal Growth Failure in Infants 501 to 1500 Grams: 2000–2013

BACKGROUND: Very low birth weight infants often gain weight poorly and demonstrate growth failure during the initial hospitalization. Although many of the major morbidities experienced by these infants during their initial NICU stays have decreased in recent years, it is unclear whether growth has improved. METHODS: We studied 362 833 infants weighing 501 to 1500 g without major birth defects born from 2000 to 2013 and who were hospitalized for 15 to 175 days at 736 North American hospitals in the Vermont Oxford Network. Average growth velocity (GV; g/kg per day) was computed by using a 2-point exponential model on the basis of birth weight and discharge weight. Postnatal growth failure and severe postnatal growth failure were defined as a discharge weight less than the 10th and third percentiles for postmenstrual age, respectively. RESULTS: From 2000 to 2013, average GV increased from 11.8 to 12.9 g/kg per day. Postnatal growth failure decreased from 64.5% to 50.3% and severe postnatal growth failure from 39.8% to 27.5%. The interquartile ranges for the hospitals participating in 2013 were as follows: GV, 12.3 to 13.4 g/kg per day; postnatal growth failure, 41.1% to 61.7%; and severe postnatal growth failure, 19.4% to 36.0%. Adjusted and unadjusted estimates were nearly identical. CONCLUSIONS: For infants weighing 501 to 1500 g at birth, average GV increased and the percentage with postnatal growth failure decreased. However, in 2013, half of these infants still demonstrated postnatal growth failure and one-quarter demonstrated severe postnatal growth failure.

Instrumental variable estimation in generalized linear measurement error models

Abstract Instrumental variable estimation in generalized linear measurement error models are studied. For models with canonical link functions, unbiased estimating equations are derived. The maximum likelihood estimator for the normal theory, structural linear instrumental variable model is shown to be a solution to the estimating equations derived herein. Logistic regression is studied in detail. An example is given and a simulation study described for the logistic model based on the Framingham Heart Study data.

Obstetric and Neonatal Care Practices for Infants 501 to 1500 g From 2000 to 2009

OBJECTIVE: To identify changes in clinical practices for infants with birth weights of 501 to 1500 g born from 2000 to 2009. METHODS: We used prospectively collected registry data for 355 806 infants born from 2000 to 2009 and cared for at 669 North American hospitals in the Vermont Oxford Network. Main outcome measures included obstetric and neonatal practices, including cesarean delivery, antenatal steroids, delivery room interventions, respiratory practices, neuroimaging, retinal exams, and feeding at discharge. RESULTS: Significant changes in many obstetric, delivery room, and neonatal practices occurred from 2000 to 2009. Use of surfactant treatment in the delivery room increased overall (adjusted difference [AD] 17.0%; 95% confidence interval [CI] 16.4% to 17.6%), as did less-invasive methods of respiratory support, such as nasal continuous positive airway pressure (AD 9.9%; 95% CI 9.1% to 10.6%). Use of any ventilation (AD –7.5%; 95% CI –8.0% to –6.9%) and steroids for chronic lung disease (AD –15.3%; 95% CI –15.8% to –14.8%) decreased significantly overall. Most of the changes in respiratory care were observed within each of 4 birth weight strata (501–750 g, 751–1000 g, 1001–1250 g, 1251–1500 g). CONCLUSIONS: Many obstetric and neonatal care practices used in the management of infants 501 to 1500 g changed between 2000 and 2009. In particular, less-invasive approaches to respiratory support increased.

Variation in Performance of Neonatal Intensive Care Units in the United States

Importance Hospitals use rates from the best quartile or decile as benchmarks for quality improvement aims, but to what extent these aims are achievable is uncertain. Objective To determine the proportion of neonatal intensive care units (NICUs) in 2014 that achieved rates for death and major morbidities as low as the shrunken adjusted rates from the best quartile and decile in 2005 and the time it took to achieve those rates. Design, Setting, and Participants A total of 408 164 infants with a birth weight of 501 to 1500 g born from January 1, 2005, to December 31, 2014, and cared for at 756 Vermont Oxford Network member NICUs in the United States were evaluated. Logistic regression models with empirical Bayes factors were used to estimate standardized morbidity ratios for each NICU. Each ratio was multiplied by the overall network rate to calculate the 10th, 25th, 50th, 75th, and 90th percentiles of the shrunken adjusted rates for each year. The proportion in 2014 that achieved the 10th and 25th percentile rates from 2005 and the number of years it took for 75% of NICUs to achieve the 2005 rates from the best quartile were estimated. Main Outcomes and Measures Death prior to hospital discharge, infection more than 3 days after birth, severe retinopathy of prematurity, severe intraventricular hemorrhage, necrotizing enterocolitis, and chronic lung disease among infants less than 33 weeks’ gestational age at birth. Results Of the 756 hospitals, 695 provided data for 2014. The mean unadjusted infant-level rate of death before hospital discharge decreased from 14.0% in 2005 to 10.9% in 2014. In 2014, 689 of 695 NICUs (99.1%; 95% CI, 97.4%-100.0%) achieved the 2005 shrunken adjusted rates from the best quartile for death prior to discharge, 678 of 695 (97.6%; 95% CI, 95.8%-99.6%) for late-onset infection, 558 of 681 (81.9%; 95% CI, 77.2%-86.6%) for severe retinopathy of prematurity, 611 of 693 (88.2%; 95% CI, 81.7%-97.0%) for severe intraventricular hemorrhage, 529 of 696 (76.0%; 95% CI, 71.8%-81.2%) for necrotizing enterocolitis, and 286 of 693 (41.3%; 95% CI, 36.1%-45.6%) for chronic lung disease. It took 3 years before 445 NICUs (75.0%) achieved the 2005 shrunken adjusted rate from the best quartile for death prior to discharge, 5 years to achieve the rate from the best quartile for late-onset infection, 6 years to achieve the rate from the best quartile for severe retinopathy of prematurity and severe intraventricular hemorrhage, and 8 years to achieve the rate from the best quartile for necrotizing enterocolitis. Conclusions and Relevance From 2005 to 2014, rates of death prior to discharge and serious morbidities decreased among the NICUs in this study. Within 8 years, 75% of NICUs achieved rates of performance from the best quartile of the 2005 benchmark for all outcomes except chronic lung disease. These findings provide a novel way to quantify the magnitude and pace of improvement in neonatology.

Unbiased scores in proportional hazards regression with covariate measurement error

Abstract This paper studies estimation of regression parameters in proportional hazards regression when covariates are subject to additive measurement error. It is shown how to construct an unbiased partial likelihood score when the moment generating function of the measurement error exists. The score is unbiased over a restriction on the parameter space where the restriction depends on the domain of definition of the moment generating function. For normal measurment error, the score is unbiased over the entire parameter space. A simulation study indicates that the score yields an estimator that is effective in reducing bias induced by covariate measurement error.

Instrumental Variable Estimation in Binary Regression Measurement Error Models

Abstract We describe two approaches to instrumental variable estimation in binary regression measurement error models. The methods entail constructing approximate mean models for the binary response as a function of the measured predictor, the instrument, and any covariates in the model. Estimates are obtained by exploiting relationships between regression parameters, just as in linear instrumental variable estimation. In the course of deriving the approximate mean models, we obtain an alternative characterization of instrumental variable estimation in linear measurement error models.

TRACKING DISPERSAL IN BIRDS: ASSESSING THE POTENTIAL OF ELEMENTAL MARKERS

Abstract Natal dispersal in vagile species such as songbirds can shape a populations range and structure. Although effective conservation practices depend on knowledge of the scale and frequency of natal dispersal, these issues remain poorly understood because of methodological gaps. In this exploratory study, we assessed whether element signatures within natal feathers might be used to identify the geographic birth site of first-year breeders. We used two related techniques, inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma with optical emission spectrometry (ICP-AES), to quantify element levels in natal feather samples from 7 species at 27 sites across the eastern United States. The techniques differed in the manner in which elements were quantified and in their detection limits. Our goal was to determine whether element analyses of feathers could discriminate (1) different species within a site and (2) different sites within a species. Additionally, because spatial autocorrelation of element levels is needed for element analysis to be an effective tool in assessing natal dispersal, we also evaluated the spatial autocorrelation of ICP-AES samples at 18 sites across the eastern United States. Both ICP-MS and ICP-AES analyses separated species within a site with fairly high accuracy, though the discriminating elements varied with site. However, within a species, natal feather locations were not identified with high accuracy on the basis of feather elements. We were not able to determine whether there is spatial correlation among individual elements or a principal component analysis (PCA) score that described the elemental makeup of a feather. A kriging model was fit to the semivariogram of PCA scores to produce a base-map of element signatures across the eastern United States. This map was ineffective at predicting feather-element values at sample sites. Whether elemental analyses can identify natal dispersal distances requires further study. We suggest that future studies evaluate elements with ICP-MS methodologies on a single, box-nesting species that is sampled more intensively at smaller geographic scale, or on species that occur in very discrete populations. Additionally, this methodology should be evaluated in concert with stable-isotope analyses of feathers and, potentially, genetic analyses. Suivre la Dispersion chez les Oiseaux: Évaluer le Potentiel de Marqueurs Élémentaires