Estimation of sampling error variance in the meta-analysis of correlations: Use of average correlation in the homogeneous case.

The estimate of the population correlation used in the formula for sampling error variance of a correlation is typically the observed correlation, but in meta-analysis the average of the observed correlations can be used. For the case in which there is no variation in the study population correlations or sample sizes and the number of studies is very large, the authors found that use of the average correlation estimator is more accurate than use of the traditional, individual correlation estimator, except in those rare cases in which the uncorrected population correlation is greater than .60. For typical sample sizes, when the uncorrected population correlation is between -.40 and .40, there is virtually no error in the meta-analysis credibility interval based on the average correlation estimator. On the other hand, the amount of the error in the individual correlation estimator is qualitatively important if the sample is 25 or less and the population correlation is less than .40. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparing squared multiple correlation coefficients: Examination of a confidence interval and a test significance.

I. Olkin and J. D. Finn (1995) presented 2 methods for comparing squared multiple correlation coefficients for 2 independent samples. In 1 method, the researcher constructs a confidence interval for the difference between 2 population squared coefficients; in the 2nd method, a Fisher-type transformation of the sample squared correlation coefficient is used to obtain a test statistic. Both methods are based on asymptotic theory and use approximations to the sampling variance. The approximations are incorrect when the population multiple correlation coefficient is zero. The 2 procedures were examined for equal and unequal population multiple correlation coefficients in combination with equal and unequal sample sizes. As expected, the procedures were inaccurate when the population multiple correlation coefficients were zero or very small and, in some conditions, were inaccurate when sample sizes and coefficients were unequal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sampling variance in the correlation coefficient under range restriction: A Monte Carlo study.

Validity generalization methods require accurate estimates of the sampling variance in the correlation coefficient when the range of variation in the data is restricted. This article presents the results of computer simulations examining the accuracy of the sampling variance estimator under sample range restrictions. Range restriction is assumed to occur by direct selection on the predictor. Sample sizes of 25, 60, and 100 are used, with the selection ratio ranging from .10 to 1.0 and the population correlation ranging from .10 to .90. The estimator is found to have a slight negative bias in unrestricted data. In restricted data, the bias is substantial in sample sizes of 60 or less. In all sample sizes, the negative bias increases as the selection ratio becomes smaller. Implications of the results for studies of validity generalization are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Averaging correlation coefficients: Should Fisher's z transformation be used?

Averaging correlations leads to underestimation because the sampling distribution of the correlation coefficient is skewed. It is also known that if correlations are transformed by Fisher's z prior to averaging, the resulting average overestimates the population value of z. The behavior of these procedures for averaging correlations was investigated via Monte Carlo simulation, both in terms of bias (under- and overestimation) and precision (standard errors). It was found that average z backtransformed to r is less biased positively than average r is biased negatively. The standard error of average r was smaller than that of average z when the population correlation was small; however, the reverse was true when the population correlation exceeded .5. Regardless of sample size, back transformed average z was always less biased; therefore, the use of the z transformation is recommended when averaging correlation coefficients, particularly when sample size is small. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Confidence intervals for the cross-validated multiple correlation in predictive regression models.

Presents improved procedures to approximate confidence intervals for ρ–2 and ρc–2 in both fixed and random predictor models. These approximations require neither point estimates nor variance estimates and are analytically shown to be precise enough for most practical prediction purposes. An application of confidence intervals in regression model development is also given. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A procedure for combining sample correlation coefficients and vote counts to obtain an estimate and a confidence interval for the population correlation coefficient.

Missing effect-size estimates pose a particularly difficult problem in meta-analysis. Rather than discarding studies with missing effect-size estimates or setting missing effect-size estimates equal to 0, the meta-analyst can supplement effect-size procedures with vote-counting procedures if the studies report the direction of results or the statistical significance of results. By combining effect-size and vote-counting procedures, the meta-analyst can obtain a less biased estimate of the population effect size and a narrower confidence interval for the population effect size. This article describes 3 vote-counting procedures for estimating the population correlation coefficient in studies with missing sample correlations. Easy-to-use tables, based on equal sample sizes, are presented for the 3 procedures. More complicated vote-counting procedures also are given for unequal sample sizes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of five rules for determining the number of components to retain.

Investigated the performance of 5 methods for determining the number of components to retain—J. L. Horn's (see record 1965-13273-001) parallel analysis, W. F. Velicer's (see record 1977-00166-001) minimum average partial (MAP), R. B. Cattell's (see PA, Vol 41:969) scree test, M. S. Bartlett's (1950) chi-square test, and H. F. Kaiser's (see record 1960-06772-001) eigenvalue greater than 1 rule—across 7 systematically varied conditions (sample size, number of variables, number of components, component saturation, equal or unequal numbers of variables for each component, and the presence or absence of unique and complex variables). Five sample correlation matrices were generated at each of 2 sample sizes from the 48 known population correlation matrices representing 6 levels of component pattern complexity. Results indicate that the performance of the parallel analysis and MAP methods was generally the best across all situations; the scree test was generally accurate but variable; and Bartlett's chi-square test was less accurate and more variable than the scree test. Kaiser's method tended to severely overestimate the number of components. (65 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

二元比例X射线荧光光谱法测定铀锆体系中铀和锆

二元比例法可依据两元素谱线的强度比与两元素浓度比的对数关系实现元素的定量分析。实验将二元比例法与X射线荧光光谱法(XRF)相结合,用于定量分析铀锆体系中铀和锆含量,不论吸收-增强效应是否严重,校准曲线都保持线性关系。对仪器的工作参数进行优化,选择铀的Lα线以及锆的Kα线作为分析线。对铀、锆标准溶液系列,先测量各工作点的X射线荧光计数率,然后分别求取浓度比和信号比的对数,再绘制二元比例校准曲线,得校准曲线的相关系数(R²)为0.999 7。对同一铀锆体系样品进行精密度考察,结果的相对标准偏差(RSD)分别为0.035%(铀)和0.048%(锆)。对6批铀锆体系样品采用实验方法进行分析,同时分别采用滴定法对铀含量、直接X射线荧光光谱法对锆含量进行比对分析,结果基本一致;对自配铀、锆二元体系样品溶液进行分析,测定值与参考值的相对误差均小于3.00%。实验方法满足铀锆体系工艺中铀和锆含量的测试要求。     

熔融制样-X射线荧光光谱法测定磁铁矿中7种组分

研究了熔融制样-X射线荧光光谱法测定磁铁矿中7种组分的分析方法。考察了稀释比、硝酸锂氧化剂用量、溴化锂脱模剂用量等因素,在优化条件下进一步选择了熔融温度及熔融时间。按试样与熔剂稀释比为1∶20在1 050 ℃熔融10 min制成玻璃样片,直接用X射线荧光光谱法(XRF)测定磁铁矿中的TFe、CaO、MgO、Al₂O₃、SiO₂、TiO₂和S。选择含铁量不同的一组磁铁矿标准样品建立校准曲线,线性相关系数均不小于0.997 4。测定磁铁矿实际样品时,测定结果与化学法一致,相对标准偏差中TFe为0.29%,S为3.4%,其它组分在0.29%～2.5%之间。     

Cloning and characterization of Rep-8 (D8S2298E) in the human chromosome 8p11.2-p12

Assessed the effect of co-occurring versus not co-occurring internalizing and externalizing behavior problems on the reasons parents reported for clinical referral of their adolescent child. Reasons for referral were coded for 181 inpatient adolescents, and parent ratings of internalizing and externalizing behavior were obtained for a general population sample of 500 adolescents. Parents concurrently reported internalizing and externalizing behavior as reasons for referral less frequently (p < .0001) than would be expected given the correlation between these two domains in the general population sample. This suggests that the presence of externalizing problems may decrease parents' concern or awareness of internalizing problems, the presence of internalizing problems may decrease parents' concern or awareness of externalizing problems, or both. Implications for the clinical referral of adolescents and for informal parental efforts at helping their children with externalizing and internalizing problems are discussed.     

Correlation between P450 CYP1A1 inducibility, MspI genotype and lung cancer incidence

The aim of this study was to verify a possible correlation between CYP1A1 induction, MspI genotype and lung cancer incidence. A case-control study was performed on 48 lung cancer patients and 81 healthy subjects to test the existence of a correlation, within a European population. The hyperinducible group exhibited a significantly higher risk of lung cancer (odds ratio = 3.41; P = 0.036), especially for adenocarcinoma (odds ratio = 5.29; P = 0.033). In contrast with the situation observed in Asian populations, the frequency of the M2 allele did not differ significantly in the total lung cancer population (7.82%) and the group of healthy subjects (10.71%). The median inducibility value was slightly higher among cancer patients with one or two M2 alleles than among patients homozygous for the wild-type allele (P = 0.09). However, the percentage of individuals possessing at least one mutated allele was not significantly higher among hyperinducible patients (37.5%) than among non-hyperinducible patients (16.0%). No significant correlation could be found between M2 allele and lung cancer or between M2 allele and CYP1A1 inducibility; the only positive correlation found was between CYP1A1 hyperinducibility and lung cancer incidence. Our observations do not support the view that the presence of the M2 allele at the MspI site of the CYP1A1 gene constitutes a significant lung cancer risk in Caucasians.     

蒸馏分离-电感耦合等离子体原子发射光谱法测定二氯氧锆中痕量和超痕量砷

提出了一种测定二氯氧锆(ZrOCl₂·8H₂O)中痕量和超痕量砷的简单而又准确的方法。根据样品中砷含量,取质量不大于10 g样品于简易蒸馏器中,加入一定量的盐酸(含少量溴化钾和硫酸亚铁),加热分解样品并蒸馏出三氯化砷,用冷水吸收后定容,在选定的仪器工作条件下,利用电感耦合等离子发射光谱法(ICP-AES)测定溶液中砷。砷的质量浓度在0.0～10.0 μg/mL与砷的响应强度值呈正比,校准曲线线性相关系数(r)大于0.999 9,样品加标回收率在99%～112%之间,相对标准偏差(RSD)在0.5%～2.0%范围(n=5)。所拟方法应用于二氯氧锆样品中痕量和超痕量砷的测定,测定值与催化极谱法或原子荧光光谱法的测定值基本一致。     

Statistical efficiency of using two quantitative randomized response techniques to estimate correlation.

Used Monte Carlo techniques to generate sampling distributions of the correlation coefficient between 2 variables, each measured by 2 quantitative models of the randomized response technique (RRT)—the additive constants model and the unrelated question model. As expected, the RRT models yielded less statistically efficient estimates of the population correlation coefficient, and inefficiency increased as the population correlation increased. Comparisons of efficiency between the 2 models favored the additive constants model for constants less than certain limiting values. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Red cell membrane fatty acids, cytosolic phospholipase-A2 and schizophrenia

Forty subjects with schizophrenia and 40 age- and sex-matched controls were recruited, and blood samples were obtained for analysis of red cell membrane fatty acid composition by capillary gas chromatography. A blood sample was also taken from the same population to test for allelic association between schizophrenia and a polymorphism close to the promoter site of the cytosolic phospholipase-A2 gene which is mapped to chromosome 1q25. The schizophrenic population was heterogeneous with regards age, symptoms severity and treatment. A significantly higher percentage concentration of dihomogamma-linolenic acid (DGLA) was found in the red cell membranes of schizophrenics compared to matched controls. All other fatty acids examined showed no difference from the normal population. No correlation was found between any demographic factor, treatment variable, diet, drug use, alcohol or tobacco consumption which could explain the biochemical findings. A negative correlation was found between the concentration of DGLA in red blood cell (RBC) membranes and severity of symptoms of schizophrenia. In particular, there was a significant correlation (r = -0.41, p = 0.009) between DGLA percentage concentrations and 'disorganised' symptoms. No association was found between schizophrenia and alleles of the polymorphism near the phospholipase-A2 gene or between fatty acid concentrations and the presence of any particular alleles. This study therefore finds support for membrane phospholipid abnormalities in patients with schizophrenia and particular symptom clusters, but does not replicate a previous report of an allelic association between a polymorphism close to the site of the cytosolic phospholipase-A2 gene and schizophrenia.     

Meta-analysis of correlation coefficients: A Monte Carlo comparison of fixed- and random-effects methods.

The efficacy of the Hedges and colleagues, Rosenthal-Rubin, and Hunter-Schmidt methods for combining correlation coefficients was tested for cases in which population effect sizes were both fixed and variable. After a brief tutorial on these meta-analytic methods, the author presents 2 Monte Carlo simulations that compare these methods for cases in which the number of studies in the meta-analysis and the average sample size of studies were varied. In the fixed case the methods produced comparable estimates of the average effect size; however, the Hunter-Schmidt method failed to control the Type I error rate for the associated significance tests. In the variable case, for both the Hedges and colleagues and Hunter-Schmidt methods, Type I error rates were not controlled for meta-analyses including 15 or fewer studies and the probability of detecting small effects was less than .3. Some practical recommendations are made about the use of meta-analysis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

熔融制样-X射线荧光光谱法测定连铸保护渣中7种组分

连铸保护渣成分构成复杂,采用粉末压片制样-X射线荧光光谱法测定时基体效应严重。实验采用将样品在1 100 ℃下灼烧2 h以测定灼烧减量,选择氧化剂NH₄NO₃在600 ℃下对样品预氧化10 min,然后将氧化后的样品、NH₄NO₃与Li₂B₄O₇-LiBO₂混合熔剂(m:m=67:33)按质量比为1:2:10的比例进行熔融制样,熔片效果良好。使用专用氧化物标准样品绘制校准曲线,以数学回归法、基本参数法和理论影响系数法消除基体效应和谱线干扰,校准曲线的相关系数均大于0.999。从而建立了熔融制样-X射线荧光光谱法快速测定连铸保护渣中SiO₂、Al₂O₃、CaO、MgO、K₂O、Na₂O和TFe的分析方法。对同一个连铸保护渣样品进行精密度考察,7种组分测定结果的相对标准偏差(RSD,n=10)均小于2%;准确度验证结果表明,实验方法的测定值与其他方法的测定值吻合较好。     

熔融制样-X射线荧光光谱法测定黑刚玉中6种组分

黑刚玉是一种以Al2O3、SiO2和TiO2为主要成分的新型环保材料,其化学成分的分析一般采用滴定法、分光光度法或原子吸收光谱法等,这些方法操作相对繁琐、流程长.实验采用H3BO3-Li2CO3混合熔剂(m∶m=7∶3)按质量比为1∶10的稀释比进行熔融制样,加入0.15 g NH4I脱模剂,有效地消除了矿物效应、粒度...     

On the bias of Huffcutt and Arthur's (1995) procedure for identifying outliers in the meta-analysis of correlations.

This study documents how the use of A. I. Huffcutt & W. A. Arthur's (1995) sample adjusted meta-analytic deviancy (SAMD) statistic for identifying outliers in correlational meta-analyses results in inaccuracies in mean r. Monte Carlo simulations found that use of the SAMD resulted in the overidentification of small relative to large correlations as outliers. Furthermore, this tendency to overidentify small correlations was found to increase as the magnitude of the population correlation increased and resulted in mean rs that overestimated the population correlation. The implications for meta-analysts are discussed, and 2 possible solutions are offered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

熔融制样-X射线荧光光谱法测定钒铁中钒硅磷锰铝铁铬镍铜

钒铁主要用作合金钢的添加剂,其化学成分的分析一般采用滴定法、分光光度法或原子吸收光谱法等,这些方法操作相对繁琐、流程长。实验采用两步法熔融制备玻璃片,即先将Li₂B₄O₇、Li₂CO₃、硝酸盐与试样混匀,在石墨粉垫底的瓷坩埚中熔融,样品熔球后转入铂黄坩埚再次熔融,建立了X射线荧光光谱法(XRF)测定钒铁合金中V、Si、P、Mn、Al、Fe、Cr、Ni、Cu含量的方法。试验表明:在Li₂B₄O₇、Li₂CO₃及试样质量比为7∶2∶0.2,脱模剂NH₄I 用量为0.5～1 g时,在1 050 ℃熔融15~20 min,熔样效果最佳。采用理论系数法对基体效应进行校正,各元素校准曲线的相关系数均大于0.996。精密度试验结果表明,钒铁中各元素测定结果的相对标准偏差(RSD,n=11)均小于4%;对实际样品进行分析时,实验方法的测定结果与其他方法的比对结果一致性较好。     

Large-sample confidence intervals for validity and reliability coefficients.

Large-sample confidence intervals (CI) for reliability, validity, and unattenuated validity are presented. The CI for unattenuated validity is based on the Bonferroni inequality, which relies on one CI for test–retest reliability and one for validity. Covered are four reliability–validity situations: (a) both estimates were from random samples; (b) reliability was from a random sample but validity was from a selected sample; (c) validity was from a random sample but reliability was from a selected sample; and (d) both estimates were from selected samples. All CIs were evaluated by using a simulation. CIs on reliability, validity, or unattenuated validity are accurate as long as selection ratio is at least 20% and selected sample size is 100 or larger. When selection ratio is less than 20%, estimators tend to underestimate their parameters. (PsycINFO Database Record (c) 2010 APA, all rights reserved)