Meta-analytic interval estimation for bivariate correlations.

The currently available meta-analytic methods for correlations have restrictive assumptions. The fixed-effects methods assume equal population correlations and exhibit poor performance under correlation heterogeneity. The random-effects methods do not assume correlation homogeneity but are based on an equally unrealistic assumption that the selected studies are a random sample from a well-defined superpopulation of study populations. The random-effects methods can accommodate correlation heterogeneity, but these methods do not perform properly in typical applications where the studies are nonrandomly selected. A new fixed-effects meta-analytic confidence interval for bivariate correlations is proposed that is easy to compute and performs well under correlation heterogeneity and nonrandomly selected studies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The organization of human abilities.

There are "two unfortunate tendencies in recent work on human abilities: the proliferation of factors and the tendency to think of only the first-order factors as the primary ones. An alternative model is to place factors in hierarchical order as advocated by the British psychometricians, especially Vernon. The application of the hierarchical model to a logical hierarchy of possible tests of mechanical information is presented, some hypothetical correlations are factored in several orders, and the Schmid-Leiman transformation is used to convert the factors back into a single orthogonal matrix manifesting the hierarchical principle. Facet analysis would enable one to define a population of tests… [and] helps restate the need for homogeneity in a test." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Meta-analysis for integrating study outcomes: A Monte Carlo study of its susceptibility to Type I and Type II errors.

AMonte Carlo study was conducted to determine Types I and II error rates of the Schmidt and Hunter (S&H) meta-analysis method and the U statistic for assessing homogeneity within a set of correlations. One thousand samples of correlations were generated randomly to fill each of 450 cells of an 18?×?5?×?5 (Underlying Population Correlations?×?Numbers of Correlations Compared?×?Sample Size Per Correlation) design. To assess Type I error rates, correlations were drawn from the same population. To assess power, correlations were drawn from two different populations. As compared with U, which was uniformly robust, the Type I error rate for the S&H method was unacceptably high in many cells, particularly when the criterion for determining homogeneity was set at a highly conservative level. Power for the S&H method increased with increasing size of population differences, sample size per correlation, and in some cases, number of correlations compared. The U statistic did more poorly in most conditions in protecting from Type II errors. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dietary magnesium intake and blood pressure: a qualitative overview of the observational studies

Published reports of 30 separate sets of analyses from 29 observational studies relating dietary intake of magnesium to blood pressure (BP) were identified through a comprehensive search using MEDLINE and BIDS-EMBASE. Three studies were prospective, 24 cross-sectional (25 reports), of which four also contained a longitudinal component, and two were obtained from baseline data in a trial. Various dietary methodologies were used: 24-h dietary recall (n = 12), food-frequency questionnaire (8), food record (7), and duplicate diet (2). Twelve reports compared magnesium intake or BP level between subgroups. Seven showed a negative association between magnesium intake and BP level, and five reported no association. From 18 of the 30 sets of analyses either a regression estimate or a Pearson correlation coefficient was reported. Many reports also allowed identification of subgroups by sex, age and race. Ninety population samples and subgroups could thus be identified from the 30 reports. All 11 Pearson-r correlation coefficients reported for systolic BP (SBP) (three significant, P < 0.05) and 10 (out of 12) Pearson-r correlation coefficients reported for diastolic BP (DBP) (four significant) were negative. Seven reports (13 subgroups for SBP, 11 subgroups for DBP) gave partial regression coefficients after adjustment; 10 (seven significant) and eight (six significant) were negative for SBP and DBP, respectively. For 13 subgroups in five papers, Pearson-r correlation coefficients were reported after adjustment for confounding factors. Eight (out of 13) showed a negative relationship for SBP and DBP. This review points to a negative association between dietary magnesium intake and BP. A systematic quantitative overview is needed to reconcile the inconsistencies of the results of individual studies and to quantify the size of such relationship.     

Clustering estimates of effect magnitude from independent studies.

One method of combining results of a series of studies is to calculate the average of the estimates of effect magnitude obtained from each study. The average estimate of effect magnitude may be misleading, however, when all studies do not share a common effect-magnitude parameter. When the effect-magnitude parameters (correlation coefficients or standardized mean differences) are heterogeneous across studies, it is often desirable to cluster studies into groups that are homogeneous with respect to the effect-size parameter. The present paper presents 2 procedures for clustering correlation coefficients and standardized mean differences when each estimator is based on the same number of observations. One procedure yields disjoint clusters and the other yields possibly overlapping clusters. In each case a method for determining the statistical significance level of the clusterings is given. Preliminary tests of homogeneity of a set of correlations or standardized mean differences are also given. The accuracy of the significance levels when estimators are based on different sample sizes is also studied. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Familial correlational analyses, sex differences, and the X-linked gene hypothesis.

The primary basis for evaluating the tenability of the X-linked hypothesis as an explanation for persistently observed sex differences on some tests has been to compare the ordering of Pearson familial test score correlations (e.g., mother–daughter, father–son) with the corresponding genetic correlations generated by an X-linked Mendelian model. Recent failures to find such a correspondence have caused the X-linked hypothesis to fall into disfavor. There are serious and apparently unrecognized problems associated with this strategy because there is no conceptual justification for it. A 4-component bivariate mixture model is proposed as a framework within which to view familial sample correlation coefficients. The expected values of the sample correlation coefficients under the model reflect other influences such as environmental determinants, not X-linked effects, even if the X-linked influences are substantial. Furthermore, the expected values of the correlation coefficients are not, in general, monotonically related to the genetic correlations. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interaction of Shallow Foundations with Reverse Faults

A series of centrifuge model tests is reported that investigated the effects of foundation position on the interaction of reverse, dip-slip faults with shallow foundations resting on sand. The model tests have allowed careful examination of both the soil and foundation deformation as a shear localization (fault) propagates through a 15?m thick sand layer for fault throws up to 5?m. By comparing results of the tests with foundations present with those from a “free-field” test, the effect of the foundation on the faulting pattern has been observed directly. The response of the foundation is very sensitive to the exact position of the fault and even when the fault emerged remotely from the foundation it sometimes caused significant foundation movements. Detailed results are presented for the tests and it is suggested that these results are used as: (1) indications of likely foundation–soil–fault interaction mechanisms; and (2) to allow future validation of numerical models for similar problems. Finally, foundation rotations measured during the fault–foundation interaction tests are compared to those predicted using a simple method based on free-field soil displacements. This simple method makes surprisingly good prediction of maximum fault rotations for different throws.     

Memory variance in the peak procedure of timing in pigeons.

Pigeons were rewarded on a fixed interval (FI) schedule. On occasional unrewarded tests, they usually showed a break–run–break pattern of responding. Across trials, the start of the run correlated positively with the end, suggesting variance across trials in (1) clock speed, (2) the delay to start the clock, or (3) a single criterion time used on a trial. If variance in criterion time exists, then a task in which the start and the end of the run are based on independent criterion times should produce a reduced start–end correlation. In 2 such tasks, the start–end correlation dropped to near zero, although other correlations were comparable to those found in the standard FI task. This provides evidence for variance across trials in a single criterion time used on a trial. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Percept-percept inflation in microorganizational research: An investigation of prevalence and effect.

Analysis of 42,934 correlations published in 581 articles not only revealed general evidence that self-report methods have produced percept–percept inflation in microresearch on organizations but also suggested that this effect is diminished when 1 or both covariates are demographic variables. Further analysis of a subsample of 11,710 correlations indicated that percept–percept inflation has influenced research on particular bivariate relationships but has not had the broad, comprehensive effects envisioned by critics. These findings challenge the validity of general condemnations of self-report methods, suggesting instead that domain-specific investigations are required to determine which areas of research are especially susceptible to percept–percept effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simulation of Varada Aquifer System for Sustainable Groundwater Development

Groundwater flow modeling has been used extensively worldwide with varying degrees of success. The ability to predict the groundwater flow is critical in planning and implementing groundwater development projects under increasing demand for fresh water resources. This paper presents the simulation of the aquifer system for planning the groundwater development of Varada basin, Karnataka, India using the Galerkin finite-element method. The government of Karnataka State, India is implementing the World Bank assisted project, “Jal Nirmal” for a sustainable development of the region, thereby ensuring a safe supply of drinking water to the northern districts of the state. Varada basin is one of the beneficiaries of the project in Haveri district. Field tests carried out in the study area indicate that the region is predominantly a confined aquifer with transmissivity and storage coefficients ranging from 5.787×10?6?m2/s (0.500?m2/day) to 4.213×10?3?m2/s (3.640×102?m2/day) and 0.011–0.001×10?2, respectively. This study mainly emphasizes the spatial and temporal variability of groundwater potential under different developmental scenarios. The model predictions were reasonably good with correlation coefficients ranging from 0.78 to 0.91 with the root mean square error of about 0.46–0.78 during calibration and validation. The stated accuracies are based on comparisons between measured and calculated heads. The outcome of the study would be a useful input for the conjunctive use of surface water and groundwater planning for the sustainable development of the region.     

Hydraulic Conductivity of MSW in Landfills

This paper presents a laboratory investigation of hydraulic conductivity of municipal solid waste (MSW) in landfills and provides a comparative assessment of measured hydraulic conductivity values with those reported in the literature based on laboratory and field studies. A series of laboratory tests was conducted using shredded fresh and landfilled MSW from the Orchard Hills landfill (Illinois, United States) using two different small-scale and large-scale rigid-wall permeameters and a small-scale triaxial permeameter. Fresh waste was collected from the working phase, while the landfilled waste was exhumed from a borehole in a landfill cell subjected to leachate recirculation for approximately 1.5 years. The hydraulic conductivity tests conducted on fresh MSW using small-scale rigid-wall permeameter resulted in a range of hydraulic conductivity 2.8×10?3–11.8×10?3?cm/s with dry unit weight varied in a narrow range between 3.9–5.1?kN/m3. The landfilled MSW tested using the same permeameter produced results between 0.6×10?3–3.0×10?3?cm/s for 4.5–5.5?kN/m3 dry unit weights. The hydraulic conductivity obtained from large-scale rigid-wall permeameter tests decreased with the increase in normal stress for both fresh and landfilled waste. The hydraulic conductivity for fresh MSW ranged from 0.2 cm/s for 4.1?kN/m3 dry unit weight (under zero vertical stress) and then decreased to 4.9×10?5?cm/s for 13.3?kN/m3 dry unit weight (under the maximum applied normal stress of 276 kPa). The hydraulic conductivity of the landfilled MSW decreased from 0.2 cm/s to 7.8×10?5?cm/s when the dry unit weight increased from 3.2 to 9.6?kN/m3. The results clearly demonstrated that the hydraulic conductivity of MSW can be significantly influenced by vertical stress and it is mainly attributed to the increase in density leading to low void ratio. In small-scale triaxial permeameter, when the confining pressure was increased from 69 to 276 kPa the hydraulic conductivity decreased from approximately 10?4?to?10?6?cm/s, which is much lower than those determined from rigid-wall permeameter tests. The published field MSW hydraulic conductivities are found to be higher than the laboratory results. Landfilled MSW possesses lower hydraulic conductivity than fresh MSW due to increased finer particles resulting from degradation. The decreasing hydraulic conductivity with increasing dry unit weight is expressed by an exponential decay function.     

Meta-Analytic Structural Equation Modeling: A Two-Stage Approach.

To synthesize studies that use structural equation modeling (SEM), researchers usually use Pearson correlations (univariate r), Fisher z scores (univariate z), or generalized least squares (GLS) to combine the correlation matrices. The pooled correlation matrix is then analyzed by the use of SEM. Questionable inferences may occur for these ad hoc procedures. A 2-stage structural equation modeling (TSSEM) method is proposed to incorporate meta-analytic techniques and SEM into a unified framework. Simulation results reveal that the univariate-r, univariate-z, and TSSEM methods perform well in testing the homogeneity of correlation matrices and estimating the pooled correlation matrix. When fitting SEM, only TSSEM works well. The GLS method performed poorly in small to medium samples. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A meta-analytic review of achievement goal measures: Different labels for the same constructs or different constructs with similar labels?

This meta-analysis addresses whether achievement goal researchers are using different labels for the same constructs or putting the same labels on different constructs. We systematically examined whether conceptual and methodological differences in the measurement of achievement goals moderated achievement goal intercorrelations and relationships with outcomes. We reviewed 243 correlational studies of self-reported achievement goals comprising a total of 91,087 participants. The items used to measure achievement goals were coded as being goal relevant (future-focused, cognitively represented, competence-related end states that the individual approaches or avoids) and were categorized according to the different conceptual definitions found within the literature. The results indicated that achievement goal–outcome and goal–goal correlations differed significantly depending on the goal scale chosen, the individual items used to assess goal strivings, and sociodemographic characteristics of the sample under study. For example, performance-approach goal scales coded as having a majority of normatively referenced items had a positive correlation with performance outcomes (r? = .14), whereas scales with a majority of appearance and evaluative items had a negative relationship (r? = ?.14). Mastery-approach goal scales that contained goal-relevant language were not significantly related to performance outcomes (r? = .05), whereas those that did not contain goal-relevant language had a positive relationship with performance outcomes (r? = .14). We concluded that achievement goal researchers are using the same label for conceptually different constructs. This discrepancy between conceptual and operational definitions and the absence of goal-relevant language in achievement goal measures may be preventing productive theory testing, research synthesis, and practical application. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Allowing for correlations between correlations in random-effects meta-analysis of correlation matrices.

Practical meta-analysis of correlation matrices generally ignores covariances (and hence correlations) between correlation estimates. The authors consider various methods for allowing for covariances, including generalized least squares, maximum marginal likelihood, and Bayesian approaches, illustrated using a 6-dimensional response in a series of psychological studies concerning prediction of exercise behavior change. Quantities of interest include the overall population mean correlation matrix, the contrast between the mean correlations, the predicted correlation matrix in a new study, and the conflict between the existing studies and a new correlation matrix. The authors conclude that accounting for correlations between correlations is unnecessary when interested in individual correlations but potentially important if concerned with a composite measure involving 2 or more correlations. A simulation study indicates the asymptotic normal assumption appears reasonable. Because of potential instability in the generalized least squares methods, they recommend a model-based approach, either the maximum marginal likelihood approach or a full Bayesian analysis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditions for positive and negative correlations between fitness and heterozygosity in equilibrium populations

The past decades have witnessed extensive efforts to correlate fitness traits with genomic heterozygosity. While positive correlations are revealed in most of the organisms studied, results of no/negative correlations are not uncommon. There has been little effort to reveal the genetic causes of these negative correlations. The positive correlations are regarded either as evidence for functional overdominance in large, randomly mating populations at equilibrium, or the results of populations at disequilibrium under dominance. More often, the positive correlations are viewed as a phenomenon of heterosis, so that it cannot possibly occur under within-locus additive allelic effects. Here we give exact genetic conditions that give rise to positive and negative correlations in populations at Hardy-Weinberg and linkage equilibria, thus offering a genetic explanation for the observed negative correlations. Our results demonstrate that the above interpretations concerning the positive correlations are not complete or even necessary. Such a positive correlation can result under dominance and potentially under additivity, even in populations where associated overdominance due to linked alleles at different loci is not significant. Additionally, negative correlations and heterosis can co-occur in a single population. Although our emphasis is on equilibrium populations and for biallelic genetic systems, the basic conclusions are generalized to non-equilibrium populations and for multi-allelic situations.     

Fe(III)–As(V) precipitates obtained from a sulphate system and their leach stability

Fe(III)–As(V) precipitates were synthesised from the Fe(II)-As(V)-SO₄^2--H₂O system at a temperature of 90°C and a constant pH maintained at 1.5?±?0.05. The precipitates obtained were characterised by X-ray diffraction (XRD), chemical composition analysis, scanning electron microscope (SEM) and Raman spectrum, thermogravimetric analyzer (TGA) and electron probe micro-analyzer (EPMA). The precipitates were in irregular aggregation of about 1–4?μm in size. The precipitates consisted of scorodite, ferric arsenate and an amorphous ferric hydroxide sulphate formulated as Fe(OH)_x(SO₄)_y. The precipitates were stable in modified Toxicity Characteristic Leaching Procedure (TCLP) tests at pH 4.93 for 60?h. Arsenic concentrations in the leaching solutions of 0.27?mg?L^?1 and 0.59?mg?L^?1 were obtained for the precipitates prepared initial Fe(II)/As(V) molar ratios of 4.0 and 5.0, respectively. Significantly more iron than arsenic was dissolved with up to 280?mg?L^?1 of iron reporting to solution. Long-term stability tests of the precipitates were carried out by leaching them for 40 days at 25°C under various media of pH between 9.50 and 10.57. The results showed that the precipitates tested in this study were more stable than those by previous researchers owing to a preferential dissolution of the amorphous ferric hydroxide sulphate.     

Convection Velocity of Vortex Structures in the Near Wake of a Circular Cylinder

The convection velocity of vortex structures in the near wake of a circular cylinder was experimentally investigated over the region 1.6–2.5 ? x/D ? 12.0 for R = 160–12,000. Dye injection technique of flow visualization and two completely noninvasive laser Doppler velocimeters were employed for R ? 320 and ?400, respectively. The convection velocity, Uc, is defined as the mean traveling velocity of vortex cores passing a streamwise separation during a mean elapsed time. For R ? 320, Uc was determined directly from the motion of dye-marked vortex cores filmed by a video camera. In the cases of R ≥ 400, the positions of peak vorticity and half of the half-velocity-defect width at each downstream section were first used to identify the mean path of vortex cores (i.e., the most probable trajectory of the vortex structures), along which spatial correlation measurements were then performed to determine the mean elapsed time corresponding to the maximum cross correlation. The present results show that, in laminar and transitional wakes, the ratio Uc/Uo increases from 0.53 to 0.84 over a region of 1.6 ? x/D ? 6.0 and then tends to be a constant of 0.84 for x/D ≥ 6.0. In a turbulent wake, Uc/Uo also increases from a certain value at a point downstream from the position of vortex formation to a mean value of about 0.86 at x/D ≥ 5.0–6.0, and then changes little with the increase of x/D. In addition, it is found that the dependence of Uc/Uo on R almost disappears for x/D ≥ 5.0.     

Determination of the Critical Strains for the Initiation of Dynamic Transformation and Dynamic Recrystallization in Four Steels of Increasing Carbon Contents

Hot torsion tests are carried on three plain carbon steels and a Nb microalloyed steel of increasing C concentrations. The tests are performed at strain rates up to 4 s^?1 and over the temperature range 743–917°C. The onsets of dynamic transformation (DT) and dynamic recrystallization (DRX) are detected using the double‐differentiation method. Both mechanisms are initiated under all testing conditions but one. The critical strain for DT increases with temperature while the reverse dependency is exhibited by the critical strain for DRX.     

Relating Batch and Column Diffusion Coefficients for Leachable Contaminants in Particulate Waste Materials

For constructed facilities in which waste materials are used as partial substitutes for traditional aggregates, it is usually necessary to perform contaminant leachability tests to assess the long-term emission of contaminants from the facilities during service. Such tests can be performed under batch and column flow-through conditions. It is usually desirable to establish the relationship between leached contaminant concentrations obtained through both tests. Using Al and Cu diffusion coefficients as the target parameter, an analytical model is developed and presented herein with experimental data from acidic solution (pH of 4.5) leach testing of asphalt concrete that was amended with municipal solid waste incinerator bottom ash in weight percentages ranging from 0 to 20 to assess the equivalence of both sets of leaching conditions. The results for Al show that at higher column flowrates indexed by Peclet numbers in excess of 5.5, there is no defined relationship between Al diffusion coefficients obtained through both methods. Fluid flow at lower Peclet numbers approach batch conditions and afford an opportunity for the use of the analytical model presented in this paper provided comparisons are made at equivalent liquid/solid ratios. The values of the batch diffusion coefficients obtained for Al are of the order of 10?10–10?6?cm2/s. For column leaching of Al, the range is 10?8–10?7?cm2/s. No measurable quantity of Cu was obtained under both batch and column leaching conditions.