Systematic Bias In Estimates Research Articles

DISSOCIATING RETEST EFFECTS FROM DEVELOPMENTAL CHANGE FOR PREDICTING COGNITIVE STATUS

Abstract In longitudinal designs, unadjusted retest effects can confound developmental change estimates. This study utilized a measurement burst design and three-level multilevel modeling to a) independently parameterize short-term retest and long-term developmental change and b) employ these estimates as predictors of cognitive status at long-term follow-ups. Using data from Project MIND , participants (N=304; aged 64-92 years) were assessed across biweekly sessions nested within annual bursts (spanning up to 17 total assessments over four years). Cognitive impairment no dementia (CIND) status was classified at Years 4 (the final burst assessment) and 8 (the study end date). Response time inconsistencies (RTI) were computed to index intraindividual variability across RT trials of a one-back response time (BRT) task. Three-level multilevel models simultaneously yet independently estimated BRT RTI change across weeks and years, indexing short-term retest and long-term developmental change, respectively. Individual slope estimates were extracted and utilized in multinomial logistic regression models contrasting short- vs. long-term RTI change as predictors of long-term cognitive status. Results from the three-level models indicated that retest and developmental slopes yielded non-redundant sources of variance, providing unique estimates of change that would otherwise be confounded. Further, short- and long-term RTI differentially predicted cognitive status at Years 4 and 8; failing to benefit from retest effects on the BRT task was associated with increased likelihood of cognitive impairment. This innovative approach to parameterizing retest effects can reduce systematic bias in estimates of long-term developmental change, as well as highlight the utility of retest effects as predictors of cognitive health.

Eliminating systematic bias from case-crossover designs.

Case-crossover designs have been widely applied to epidemiological and medical investigations of associations between short-term exposures and risk of acute adverse health events. Much effort has been made in literature on understanding source of confounding and reducing systematic bias by reference-select strategies. In this paper, we explored the nature of bias in the ambi-directional and time-stratified case-crossover designs via simulation using actual air pollution data from urban Edmonton, Alberta, Canada. We further proposed a calibration approach for eliminating systematic bias in estimates (coefficient estimate, 95% confident interval, and p-value). Bias check for coefficient estimation, size check and power check for significance test were done via simulation experiments to show advantages of the calibrated case-crossover studies over the ones without calibration. An application was done to investigate associations between air pollutants and acute myocardial infarction hospitalizations in urban Edmonton. In conclusion, systematic bias in a case-crossover design is often unavoidable, leading to an obvious bias in the estimated effect and an unreliable p value in the significance test. The proposed calibration technique provides an efficient approach to eliminating systematic bias in a case-crossover study.

Cohort Trends in the Gender Distribution of Household Tasks in the United States and the Implications for Understanding Disability.

Objectives: Measures of disability depend on health and social roles in a given environment. Yet, social roles can change over time as they have by gender. We document how engagement in Instrumental Activities of Daily Living (IADLs) is shifting by gender and birth cohort among older adults, and the challenges these shifts can create for population-level estimates of disability. Method: We used the Health and Retirement Study (N = 25,047) and multinomial logistic regression models with an interaction term between gender and birth cohort to predict limitation and nonperformance relative to no difficulty conducting IADLs. Results: Nonperformance of IADLs have significantly decreased among younger cohorts. Women in younger cohorts were more likely to use a map, whereas men in younger cohorts were more likely to prepare meals and shop. Discussion: Failing to account for gender and cohort changes in IADL, performance may lead to systematic bias in estimates of population-level disability.

Precision of Calcified Structures Used for Estimating Age of Chain Pickerel

AbstractWith the exception of Northern Pike Esox lucius, there is a paucity of information on the precision of age estimates based on calcified structures for esocid species, especially Chain Pickerel E. niger. We estimated ages for 42 Chain Pickerel from Stevens Creek Reservoir on the Savannah River, South Carolina–Georgia. Ages were estimated using sectioned pelvic, pectoral, dorsal, and anal fin rays, scales, cleithra (sectioned and whole), and otoliths to assess precision between repeated readings (four readers). Precision was evaluated by calculating agreement among readers, CV, and mean absolute difference (MAD) in estimates between reader pairs. We tested for differences in precision of estimates among structures using linear mixed models with CV or MAD as the response. Finally, we used age bias plots to evaluate whether there were structure or reader‐related systematic biases in estimates. Coefficient of variation and MAD were significantly related to structure type (CV: P = 0.006, MAD: P = 0.001) and mean estimated age (CV: P < 0.001, MAD: P = 0.025). Precision was poor for all structures and poorest for age‐0 fish; however, all analyses indicated that otoliths provided the most precise estimates. We observed agreement in estimates among all readers for 40% of the otoliths examined and consensus agreement for 74% of the estimates. Coefficient of variation for otoliths declined from 67% for fish with a mean estimated age of 0 years to 5% for age‐4 fish. Conversely, MAD for otoliths increased from 0.34 years for fish with a mean estimated age of 0 to 0.46 years for age‐4 fish. Estimates from all structures, except pectoral rays, were negatively biased compared with estimates from otoliths. We recommend the use of otoliths for age estimation of Chain Pickerel, but managers and researchers should be cognizant of and evaluate the potential effects of variability in age estimates among readers on their analyses.

Effects of nonquadrupole modes in the detection and parameter estimation of black hole binaries with nonprecessing spins

We study the effect of nonquadrupolar modes in the detection and parameter estimation of gravitational waves (GWs) from black hole binaries with nonprecessing spins, using Advanced LIGO. We evaluate the loss of the signal-to-noise ratio (SNR) and the systematic errors in the estimated parameters when a quadrupole-mode template family is used to detect GW signals with all the relevant modes. Target signals including nonquadrupole modes are constructed by matching numerical-relativity simulations of nonprecessing black hole binaries describing the late inspiral, merger and ringdown with post-Newtonian/effective-one-body waveforms describing the early inspiral. We find that neglecting nonquadrupole modes will, in general, cause unacceptable loss in the detection rate and unacceptably large systematic errors in the estimated parameters, for the case of massive binaries with large mass ratios. For a given mass ratio, neglecting subdominant modes will result in a larger loss in the detection rate for binaries with aligned spins. For binaries with antialigned spins, quadrupole-mode templates are more effectual in detection, at the cost of introducing a larger systematic bias in the parameter estimation. We provide a summary of the regions in the parameter space where neglecting nonquadrupole modes will cause an unacceptable loss of detection rates and unacceptably large systematic biases in the estimated parameters.

Eccentricity samples: Implications on the potential and the velocity distribution

Planar and vertical epicycle frequencies and local angular velocity are related to the derivatives up to the second order of the local potential and can be used to test the shape of the potential from stellar disc samples. These samples show a more complex velocity distribution than halo stars and should provide a more realistic test. We assume an axisymmetric potential allowing a mixture of independent ellipsoidal velocity distributions, of separable or Staeckel form in cylindrical or spherical coordinates. We prove that values of local constants are not consistent with a potential separable in addition in cylindrical coordinates and with a spherically symmetric potential. The simplest potential that fits the local constants is used to show that the harmonical and non-harmonical terms of the potential are equally important. The same analysis is used to estimate the local constants. Two families of nested subsamples selected for decreasing planar and vertical eccentricities are used to borne out the relation between the mean squared planar and vertical eccentricities and the velocity dispersions of the subsamples. According to the first-order epicycle model, the radial and vertical velocity components provide accurate information on the planar and vertical epicycle frequencies. However, it is impossible to account for the asymmetric drift which introduces a systematic bias in estimation of the third constant. Under a more general model, when the asymmetric drift is taken into account, the rotation velocity dispersions together with their asymmetric drift provide the correct fit for the local angular velocity. The consistency of the results shows that this new method based on the distribution of eccentricities is worth using for kinematic stellar samples.

Pacific Salmon Prespawn Mortality: Patterns, Methods, and Study Design Considerations

Adult Pacific salmon Oncorhynchus spp. may reach spawning grounds but perish before reproducing, a phenomenon known as “prespawn mortality” (PSM). This review synthesizes information on PSM rates and estimation methods to evaluate patterns and facilitate study design development. Questionnaire responses from 60 fisheries professionals indicated that female PSM was routinely monitored in numerous Pacific salmon populations, but variations in data collection and reporting could lead to systematic biases in estimates. Reported PSM rates varied among years and locations, ranging from 0% to over 90%. An evaluation of methodological variations within a single data set illustrated that PSM estimates were sensitive to estimation method, the timing and spatial extent of sampling, and inclusion of male data. To improve accuracy of PSM estimates based on carcass data, we recommend frequent surveys during holding and spawning periods, use of spatially and temporally balanced study designs with adequate sample sizes, and separate reporting for males and females.

Analytical model for non-thermal pressure in galaxy clusters – II. Comparison with cosmological hydrodynamics simulation

Turbulent gas motion inside galaxy clusters provides a non-negligible non-thermal pressure support to the intracluster gas. If not corrected, it leads t o a systematic bias in the estimation of cluster masses from X-ray and Sunyaev-Zel’dovich (SZ) obse rvations assuming hydrostatic equilibrium, and affects interpretation of measurements of the SZ power spectrum and observations of cluster outskirts from ongoing and upcoming large cluster surveys. Recently, Shi & Komatsu (2014) developed an analytical model for predicting the radius, mass, and redshift dependence of the non-thermal pressure contributed by the kinetic random motions of intracluster gas sourced by the cluster mass growth. In th is paper, we compare the predictions of this analytical model to a state-of-the-art cosmol ogical hydrodynamics simulation. As different mass growth histories result in different non- thermal pressure, we perform the comparison on 65 simulated galaxy clusters on a cluster-by-cluster basis. We find an excellent agreement between the modeled and simulated non-thermal pressure profiles. Our results open up the possibility of using the analytical model to correct the systematic bias in the mass estimation of galaxy clusters. We also discuss tests of the p hysical picture underlying the evolution of intracluster turbulence, as well as a way to fur ther improve the analytical modeling, which may help achieve a unified understanding of non- thermal phenomena in galaxy clusters.

Neighborhood Contexts, Health, and Behavior: Understanding the Role of Scale and Residential Sorting

Recent reviews in sociology, public health, and urban planning suggest small-scale geographic variations in urban environments are associated with an individual's health, behavior, and well-being. However, estimation of these ‘neighborhood effects' are complicated. One complicating factor is residential sorting: Individual characteristics such as race, age, and socioeconomic status are associated with behavior and health and these same individual-level factors are often geographically clustered within neighborhoods. This residential sorting leads to a correlation between individual and environmental determinants of behavior and health and poses problems for statistical inference. A second complicating factor is uncertainty about the geographic dimensions of a person's neighborhood. We explore these two potential confounders through a simulation experiment that generates synthetic cityscapes and synthetic behaviors for geolocated individuals. The simulation is used to develop a model of how residential sorting, urban structure, and the geographic definition of an individual's neighborhood affect our understanding of the association between the urban environment and behavior. We find that residential sorting does not systematically affect the magnitude of neighborhood effect estimates, however, the misrepresentation of the geographic dimensions of an individual's neighborhood leads to systematic bias in estimates of neighborhood effects. Unlike previous research on the modifiable areal unit problem we find a systematic relationship between the definition of geographic units of analysis and the magnitude of regression coefficients.

The allocation of ecosystem net primary productivity in tropical forests

The allocation of the net primary productivity (NPP) of an ecosystem between canopy, woody tissue and fine roots is an important descriptor of the functioning of that ecosystem, and an important feature to correctly represent in terrestrial ecosystem models. Here, we collate and analyse a global dataset of NPP allocation in tropical forests, and compare this with the representation of NPP allocation in 13 terrestrial ecosystem models. On average, the data suggest an equal partitioning of allocation between all three main components (mean 34 ± 6% canopy, 39 ± 10% wood, 27 ± 11% fine roots), but there is substantial site-to-site variation in allocation to woody tissue versus allocation to fine roots. Allocation to canopy (leaves, flowers and fruit) shows much less variance. The mean allocation of the ecosystem models is close to the mean of the data, but the spread is much greater, with several models reporting allocation partitioning outside of the spread of the data. Where all main components of NPP cannot be measured, litterfall is a good predictor of overall NPP (r(2) = 0.83 for linear fit forced through origin), stem growth is a moderate predictor and fine root production a poor predictor. Across sites the major component of variation of allocation is a shifting allocation between wood and fine roots, with allocation to the canopy being a relatively invariant component of total NPP. This suggests the dominant allocation trade-off is a 'fine root versus wood' trade-off, as opposed to the expected 'root-shoot' trade-off; such a trade-off has recently been posited on theoretical grounds for old-growth forest stands. We conclude by discussing the systematic biases in estimates of allocation introduced by missing NPP components, including herbivory, large leaf litter and root exudates production. These biases have a moderate effect on overall carbon allocation estimates, but are smaller than the observed range in allocation values across sites.

Measuring Energy Subsidies Using the Price-Gap Approach: What Does it Leave Out?

In Price Subsidies Using the Price-Gap Approach: What Does it Leave Out? prepared under the International Institute for Sustainable Development’s (IISD) Bali to Copenhagen project, Doug Koplow looks at the most commonly employed methodology for estimating fossil-fuel subsidies, the ‘price-gap’ method. The report explains how the price-gap method works, reviews its benefits and limitations, and explores potential systematic bias in estimates, drawing conclusions and implications for their interpretation. Among its key findings are: Price-gap data are basic information needed to estimate support to producers and consumers, and should be collected annually for all major fossil-fuel energy producing and consuming nations. Measuring the price-gap does not capture everything. Reliance on only price-gap data will dramatically understate the magnitude of fossil-fuel subsidies globally, as it fails to capture subsidy flows that do not change fuel prices. The ‘transfer method’, which quantifies all subsidy flows conferred by a country’s fossil fuel policy interventions, is more difficult to complete but can help ‘fill in’ some of these gaps. Transfer studies should be conducted every five years in the top ten fossil-energy producing and consuming nations, as well as countries who derive large portions of their GDP from extractive industries.

Nuclear gene phylogeography using PHASE: dealing with unresolved genotypes, lost alleles, and systematic bias in parameter estimation

BackgroundA widely-used approach for screening nuclear DNA markers is to obtain sequence data and use bioinformatic algorithms to estimate which two alleles are present in heterozygous individuals. It is common practice to omit unresolved genotypes from downstream analyses, but the implications of this have not been investigated. We evaluated the haplotype reconstruction method implemented by PHASE in the context of phylogeographic applications. Empirical sequence datasets from five non-coding nuclear loci with gametic phase ascribed by molecular approaches were coupled with simulated datasets to investigate three key issues: (1) haplotype reconstruction error rates and the nature of inference errors, (2) dataset features and genotypic configurations that drive haplotype reconstruction uncertainty, and (3) impacts of omitting unresolved genotypes on levels of observed phylogenetic diversity and the accuracy of downstream phylogeographic analyses.ResultsWe found that PHASE usually had very low false-positives (i.e., a low rate of confidently inferring haplotype pairs that were incorrect). The majority of genotypes that could not be resolved with high confidence included an allele occurring only once in a dataset, and genotypic configurations involving two low-frequency alleles were disproportionately represented in the pool of unresolved genotypes. The standard practice of omitting unresolved genotypes from downstream analyses can lead to considerable reductions in overall phylogenetic diversity that is skewed towards the loss of alleles with larger-than-average pairwise sequence divergences, and in turn, this causes systematic bias in estimates of important population genetic parameters.ConclusionsA combination of experimental and computational approaches for resolving phase of segregating sites in phylogeographic applications is essential. We outline practical approaches to mitigating potential impacts of computational haplotype reconstruction on phylogeographic inferences. With targeted application of laboratory procedures that enable unambiguous phase determination via physical isolation of alleles from diploid PCR products, relatively little investment of time and effort is needed to overcome the observed biases.

전화조사의 체계적 편향 - 2007년 대통령선거 여론조사들에 대한 메타분석 -

2007년 12월의 대통령선거 과정에서 행해진 수많은 전화 여론조사에서 이명박 후보가 일관되게 앞자리를 지켰다. 많은 수의 여론조사가 시행되는 경우 개별 여론조사의 표본추출오차는 상쇄되어 소멸한다. 그러나 일정한 편향은 많은 수의 조사가 실행된다 하더라도 잔존하므로 중요한 문제가 아닐 수 없다. 우리나라의 전화조사는 지역, 성과 연령대를 고려한 할당추출(quota sampling)을 사용하며 대부분 전화번호부를 표집 틀로 한다. 조사 거절률도 높은 편이다. 이에 따라 조사표본들이 할당변인 외의 인구사회적 속성에서 모집단을 잘 대표하지 못할 수 있다. 이 연구의 목적은 허명회 등 (2004)의 연구 방법른을 2007년에 수행된 대통령선거 여론조사 L8개 사례에 적용하여 다음 물음에 답하는 데 목적이 있다. - 물음 1. 각후보에 대한 선호도 또는 지지율에 체계적 편향이 있지 않았는가? - 물음 2. 편향이 있었다면, 그 원인이 어디에 있는가? 첫째 물음에 답하기 위하여 2007년 11월 이후 시행된 11개 사례 자료에 지역, 성과 연령대 외에 직업과 학력까지 고려한 반복비례가중법(rim weighting)을 적용해보았다. 그 결과, 이명박 후보의 지지율이 평균 1.4%P 과다 추정되었던 것으로 나타났다. 반면, 정동영 후보의 지지율은 평균 0.6%P 과소 추정되었고 이에 따라 두 후보간 지지율 차이가 2.0%P (= 1.4+0.6) 과다하게 추정되었던 것으로 보여진다. 둘째 물음에 답하기 위하여 위의 11개 사례 자료에서 이명박 후보 지지를 종속변수로 하는 로지스틱 회귀 분석을 하였다. 그 결과, 전화조사 표본에서의 저학력자 과소 및 가정주부의 과다가 이명박 편향의 원인이 되는 것으로 밝혀졌다. For 2007 Korea presidential election, most polls by telephone surveys indicated Lee Myung-Bak led the second runner-up Jung Dong-Young by certain margin. The margin between two candidates can be estimated accurately by averaging individual poll results, provided there exists no systematic bias in telephone surveys. Most Korean telephone surveys via telephone directory are based on quota samples, with the region, the gender and the age-band as quota variables. Thus the surveys may result in certain systematic bias due to unbalanced factors inherent in quota sampling. The aim of this study is to answer the following questions by the analytic methods adopted in Huh et al. (2004): Question 1. Wasn't there systematic bias in estimates of support rates. Question 2. If yes, what was the source of the bias? To answer the questions, we collected eighteen surveys administered during the election campaign period and applied the iterated proportional weighting (the rim weighting) to the last eleven surveys to obtain the balance in five factors - region, gender, age, occupation and education level. We found that the support rate of Lee Myung-Bak was over-estimated consistently by 1.4%P and that of Jung Dong-Young was underestimated by 0.6%P, resulting in the over-estimation of the margin by 2.0%P. By investigating the Lee Myung-Bak bias with logistic regression models, we conclude that it originated from the under-representation of less educated class and/or the over-representation of house wives in telephone samples.

Dealing with virtual aggregation – a new index for analysing heterogeneous point patterns

Point pattern analyses such as the estimation of Ripley's K‐function or the pair‐correlation function g are commonly used in ecology to characterise ecological patterns in space. However, a major disadvantage of these methods is their missing ability to deal with spatial heterogeneity. A heterogeneous intensity of points causes a systematic bias in estimates of the K‐ and g‐functions, a phenomenon termed “virtual aggregation” in the recent literature.To address this problem, we derive a new index, called K2‐index, as an extension of existing point pattern characteristics. The K2‐index has a heuristic interpretation as an approximation to the first derivative of the g‐function.We estimate the K‐, g‐ and K2‐functions for six different types of simulated point patterns and show that the K2‐index may provide important information on point patterns that the other methods fail to detect. The results indicate that particularly the small‐scale distributions of points are better represented by the K2‐index. This might be important for testing hypotheses on ecological processes, because most of these processes, such as direct neighbour interactions, occur very locally.When applied to empirical patterns of molehill distribution, the results of the K2‐analysis show regularity up to distances between 0.1 and 0.4 m in most of the study areas, and aggregation of molehills up to distances between 0.2 and 1.1 m. The type and scale of these deviations from randomness agree with a priori expectations on the hill‐building behaviour of moles. In contrast, the estimated g‐functions merely indicate aggregation at the full range from 0 to 7 m (or even above).Considering the advantages and disadvantages of the different methods, we suggest that the K2‐index should be used as a complement to existing approaches, particularly for point patterns generated by processes that act on more than one scale.

Toward a minimum change model for recent plate motions: calibrating seafloor spreading rates for outward displacement

SUMMARY We use seafloor spreading distances derived from reconstructions of more than 7000 crossings of young magnetic anomalies along seven plate boundaries to study outward displacement, a source of systematic bias in estimates of seafloor spreading rates, which is caused by a combination of processes that shift magnetic polarity transition zones away from their idealized locations. Linear regressions of 81 independent sequences of seafloor opening distances as a function of their magnetic reversal ages for anomalies younger than C3n.1 (4.19 Ma) yield 75 positively valued intercepts for zero seafloor age, confirming the ubiquitous outward shift of magnetic reversals reported by previous authors. Grouping these data into 29 locally consistent clusters yields better constrained zero-age intercepts that are uniformly positive and average 2.2 ± 0.3 km globally. These values, which are 1–3 km at most locations and are significantly larger (3–5 km) along the well-surveyed Reykjanes and Carlsberg ridges, agree well with published magnetic polarity zone transition widths, which are estimated directly from nearbottom seafloor magnetic measurements. Significant variations in outward displacement along the Southeast Indian Ridge are strongly correlated with changes in axial morphology and axial depth; however, a similar correlation is not observed along other ridges. Forward magnetic anomaly modelling suggests that variations in outward displacement can be explained by differences in the magnetic source layers that are assumed to characterize different spreading centres. If not corrected for outward displacement, the implied systematic upward biases in seafloor spreading rates, which are averaged over the width of Anomaly 1—the youngest reversal that is used for plate reconstructions—range from 6 mm yr −1 along the Reykjanes Ridge, where outward displacement is 4–5 km, to 3 mm yr −1 along ridges where outward displacement approximates the global average of 2 km.

Resolving systematic errors in estimates of net ecosystem exchange of CO 2 and ecosystem respiration in a tropical forest biome

The controls on uptake and release of CO 2 by tropical rainforests, and the responses to a changing climate, are major uncertainties in global climate change models. Eddy-covariance measurements potentially provide detailed data on CO 2 exchange and responses to the environment in these forests, but accurate estimates of the net ecosystem exchange of CO 2 (NEE) and ecosystem respiration ( R eco) require careful analysis of data representativity, treatment of data gaps, and correction for systematic errors. This study uses the comprehensive data from our study site in an old-growth tropical rainforest near Santarem, Brazil, to examine the biases in NEE and R eco potentially associated with the two most important sources of systematic error in Eddy-covariance data: lost nighttime flux and missing canopy storage measurements. We present multiple estimates for the net carbon balance and R eco at our site, including the conventional “ u* filter”, a detailed bottom-up budget for respiration, estimates by similarity with 222Rn, and an independent estimate of respiration by extrapolation of daytime Eddy flux data to zero light. Eddy-covariance measurements between 2002 and 2006 showed a mean net ecosystem carbon loss of 0.25 ± 0.04 μmol m −2 s −1, with a mean respiration rate of 8.60 ± 0.11 μmol m −2 s −1 at our site. We found that lost nocturnal flux can potentially introduce significant bias into these results. We develop robust approaches to correct for these biases, showing that, where appropriate, a site-specific u* threshold can be used to avoid systematic bias in estimates of carbon exchange. Because of the presence of gaps in the data and the day–night asymmetry between storage and turbulence, inclusion of canopy storage is essential to accurate assessments of NEE. We found that short-term measurements of storage may be adequate to accurately model storage for use in obtaining ecosystem carbon balance, at sites where storage is not routinely measured. The analytical framework utilized in this study can be applied to other Eddy-covariance sites to help correct and validate measurements of the carbon cycle and its components.

Bias and asymmetric loss in expert forecasts: A study of physician prognostic behavior with respect to patient survival

We study the behavioral processes undergirding physician forecasts, evaluating accuracy and systematic biases in estimates of patient survival and characterizing physicians’ loss functions when it comes to prediction. Similar to other forecasting experts, physicians face different costs depending on whether their best forecasts prove to be an overestimate or an underestimate of the true probabilities of an event. We provide the first empirical characterization of physicians’ loss functions. We find that even the physicians’ subjective belief distributions over outcomes are not well calibrated, with the loss characterized by asymmetry in favor of over-predicting patients’ survival. We show that the physicians’ bias is further increased by (1) reduction of the belief distributions to point forecasts, (2) communication of the forecast to the patient, and (3) physicians’ own past experience and reputation.

Meta-analytic evidence of systematic bias in estimates of neuroleptic malignant syndrome incidence

Objective The aim of this study was to examine published reports for sources of excessive variance in neuroleptic malignant syndrome (NMS) incidence estimates. Data Sources An unrestricted computerized MEDLINE search was conducted with a comprehensive search logic and supplemented by secondary references and a manual search of an extensive personal library. Study Selection Studies were analyzed if they presented original data and provided at least 2 of the following: number of NMS cases, number of patients at risk, or ratio of cases to patients at risk. Twenty-six of the 28 candidate studies met these minimal criteria. Data Extraction Variables included incidence, year of study publication, mean year of NMS occurrence, patient population at risk, study design, diagnostic criteria, and country of origin. Data Synthesis Standard error, which reflects study size, accounted for 90.8% of the variance ( β = .953, P < .001) in this international series of 26 NMS incidence estimates. Incidence was significantly lower in 7 studies the time end points of which were set in advance of case identification ( χ 2 = 71.08, P ≪ .001). No other variable was significantly related to incidence. Conclusions Neuroleptic malignant syndrome incidence estimates to date are non–trivially biased such that larger study size (patients at risk) is strongly related to lower observed incidence. Future studies can minimize the contribution of this and other sources of experimental error by incorporating several very feasible recommendations.

Systematic bias in estimates of reproductive potential of an Atlantic cod (Gadus morhua) stock: implications for stock–recruit theory and management

Stock–recruit relationships that use spawning stock biomass (SSB) to represent reproductive potential assume that the proportion of SSB composed of females and the relative fecundity (number of eggs produced per unit mass) are both constant over time. To test these two assumptions, female-only spawner biomass (FSB) and total egg production (TEP) were estimated for the Northeast Arctic stock of Atlantic cod (Gadus morhua) over a 56-year time period. The proportion of females (FSB/SSB) varied between 24% and 68%, and the variation was systematic with length such that SSB became more female-biased as the mean length of spawners increased. Relative fecundity of the stock (TEP/SSB) varied between 115 and 355 eggs·g–1and was significantly, positively correlated with mean length of spawners. Both FSB and TEP gave a different interpretation of the recruitment response to reductions in stock size (overcompensatory) compared with that obtained using SSB (either compensatory or depensatory). There was no difference between SSB and FSB in the assessment of stock status; however, in recent years (1980–2001) TEP fell below the threshold level at which recruitment becomes impaired more frequently than did SSB. This suggests that using SSB as a measure of stock reproductive potential could lead to overly optimistic assessments of stock status.

The impact of locomotor energetics on mammalian foraging

The ecological impact of energy expended on an activity stems from its effect on foraging requirements. For locomotion, the effect of moving each additional unit distance probably depends on the proportional increase in energy expenditure. Other common measures of the cost of locomotion do not reflect the impact of energy expenditure on foraging requirements. In terrestrial mammals, both the effect of body mass and the unit cost itself are very small: moving one kilometre requires less than 2% of all other energy expenditures combined. Total locomotor energy expenditure ranges from 1/2% of daily metabolism for a 10 g mammal to 6% for an elephant. Potential sources of bias in the estimation of these costs include systematic bias in estimates of distance traversed and extra energy required for non‐linear locomotion. Because larger mammals can readily locomote at greater speeds, the primary locomotor advantage of large size may not be conservation of energy but of time, which can mean greater safety and more or better food.