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Results for “correlation matrix”

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PubMed1998

Application of GEE procedures for sample size calculations in repeated measures experiments.

Derivation of the minimum sample size is an important consideration in an applied research effort. When the outcome is measured at a single time point, sample size procedures are well known and widely applied. The corresponding situation for longitudinal designs, however, is less well developed. In this paper, we adapt the generalized estimating equation (GEE) approach of Liang and Zeger to sample size calculations for discrete and continuous outcome variables. The non-central version of the Wald Chi 2 test is considered. We use the damped exponential family of correlation structures described in Muñoz et al. for the 'working' correlation matrix among the repeated measures. We present a table of minimum sample sizes for binary outcomes, and discuss extensions that account for unequal allocation, staggered entry and loss to follow-up.

Bias↗

PubMed1998

The analysis of complex patterns of longitudinal binary response: an example of transient dysphagia following radiotherapy.

In many clinical trials, treatment is given in phases and the prevalence of symptoms is recorded longitudinally. As a result, complex non-linear response patterns may be observed as the prevalence of symptoms changes as a consequence of treatment. In such cases, although profiles of the marginal response over time give an informative description of the data, they do not allow a formal treatment comparison or adjustment for covariates of interest. Here we analyse previously reported data on transient dysphagia in patients with non-small-cell lung cancer treated with radiotherapy. We use a generalized estimating equation approach for repeated measurement binary response to give robust standard errors taking account of the dependence of observations taken on the same subject, alongside a natural cubic spline to represent the complex shape of the marginal response. This provides a reasonable model for the marginal response and allows unbiased estimation of an apparent treatment difference. The effect of different choices for the working correlation matrix is discussed, as is the modelling of treatment group differences that vary over time. We conclude that these models provide a powerful tool for the analysis of such data that can now be applied using generally accessible software.

Carcinoma, Non-Small-Cell Lung↗

PubMed1998

Factor analysis of the WISC-R (Spanish version) at 11 age levels between 6 1/2 and 16 1/2 years.

The Spanish version of the Wechsler Intelligence Scale for Children-Revised (WISC-R, Wechsler, 1974)-the Escala de Inteligencia para Niños-Revision (EIWN-R, Wechsler, 1982)-has a potentially important role in the assessment of Hispanic children. However, little is known regarding its psychometric characteristics. This study used the normative data from the EIWN-R standardization sample (N = 532 Cuban Americans) to examine its factorial composition and general comparability with the WISC-R. Within each of the 11 age groups (ages 6 1/2 to 16 1/2), the correlation matrix of raw scores was subjected to a principal components analysis and varimax rotation. The results supported a 2-factor solution across age groups roughly corresponding with Wechsler's verbal and performance dimensions. The existence of a meaningful third factor, which has empirical support in the WISC-R literature, failed to emerge for the EIWN-R.

Adolescent↗

PubMed1997

Convergent and divergent validity of the Beck Anxiety Inventory for patients with panic disorder and agoraphobia.

Psychometric properties of the Beck Anxiety Inventory (BAI) (Beck and Steer, 1990) were investigated in a sample of 82 patients suffering from panic disorder with agoraphobia. Before and after brief treatment, patients completed a battery of questionnaires and, for 2-week periods, kept a daily panic diary in which they recorded panic attacks, fear of panic, and average anxiety. The BAI demonstrated excellent internal consistency and good test-retest reliability over a 5-week interval. A partial multitrait, multimethod correlation matrix provided evidence of convergent validity with other measures of anxiety and of divergent validity vis á vis measures of depression. Factor analyses of pretest scores and residual gain scores used to address criticism that the BAI is excessively panic-centric yielded mixed results. In one analysis, the BAI was loaded with multimethod measures of panic and anxiety and, in the other, with questionnaire methods of assessing anxiety and depression. However, the BAI was clearly distinguished from measures of fear of fear, a central construct in panic disorder, and agoraphobic avoidance. Finally, the BAI proved sensitive to change with treatment, yielding effect sizes for improvement comparable to those of other anxiety measures.

Adult↗

PubMed2000

Is there a g factor for fitness?

Biological fitness is a directly observable quantity with well-known causal components, in contrast to the latent 'g' factor of psychometrics. The study of the causes of variation in fitness should therefore be simpler than the study of variation in mental abilities, but a paucity of data has kept the nature of genetic variation in fitness obscure. We can define an 'f' factor as variation creating positive correlations among components of fitness. There is little doubt that such f factor exist. Perturbations of populations such as mutation or environmental change create such patterns of positive correlation. However, natural selection will tend to minimize variation in any f factor, so it is much less clear whether f causes quantitatively substantial genetic variation within populations. Experimental data are consistent with variation in an f factor within some natural populations. As predicted, f is less important in populations where natural selection has had more opportunity to reshape the correlation matrix. Although one can incorporate variation in g into a study of variation in human fitness, the pace of change in our environment suggests that the results would neither reflect the conditions under which g evolved nor predict future evolutionary changes in g.

Factor Analysis, Statistical↗

PubMed1988

A multifactor model of the Halstead-Reitan Neuropsychological Test Battery and its relationship to cognitive status and psychiatric diagnosis.

An oblique, five-factor model of a modified Halstead-Reitan Neuropsychological Test Battery is presented. One hundred fifty-one neuropsychiatric inpatients (94 men, 57 women) were examined on 44 neuropsychological indices. Five correlated dimensions (r = .25), viz., Verbal Comprehension, Perceptual Organization, Sensory-attention, Primary Motor, and Tactile-spatial abilities, were identified by maximum likelihood factor analyses of this correlation matrix. These findings are quite similar to those reported earlier by Fowler, Richards, Berent, and Boll (1985, 1987) and Royce, Yeudall, and Bock (1976). The factors may be broadly categorized using the distinction made by Lezak (1983) for verbal, nonverbal, and mental activity variables. MANOVAs revealed systematic relationships between simple-weighted factor scores and: (1) the overall level of cognitive functioning (p less than .01), as well as (2) psychiatric diagnosis (p less than .01). Implications of these findings for understanding the impact of neuropsychiatric disorders on the structure of abilities for such patients are developed.

Adult↗

PubMed1993

Predicting Wechsler Adult Intelligence Scale-Revised (WAIS-R) IQ scores from the Luria-Nebraska Neuropsychological Battery (Form I).

The study examined a modification of two sets of previously published LNNB-derived WAIS IQ estimates in order to estimate WAIS-R IQs in a sample of neuropsychiatric patients. Findings suggested that the modification will allow practicing clinicians to estimate WAIS-R IQs with a level of accuracy similar to that found in previous research. The level of predictive accuracy for WAIS-R FSIQ and VIQ was somewhat higher than would be expected on the basis of previous research, which suggests that the modified McKay, Golden, Moses, Fishburne, and Wisniewski (1981) formulae for estimating IQ may be more accurate than previously thought. The correlation matrix of WAIS-R subtests and LNNB Form I clinical and summary scales also is described.

Adult↗

PubMed2004

Brain structure variation in great apes, with attention to the mountain gorilla (Gorilla beringei beringei).

This report presents data regarding the brain structure of mountain gorillas (Gorilla beringei beringei) in comparison with other great apes. Magnetic resonance (MR) images of three mountain gorilla brains were obtained with a 3T scanner, and the volume of major neuroanatomical structures (neocortical gray matter, hippocampus, thalamus, striatum, and cerebellum) was measured. These data were included with our existing database that includes 23 chimpanzees, three western lowland gorillas, and six orangutans. We defined a multidimensional space by calculating the principal components (PCs) from the correlation matrix of brain structure fractions in the well-represented sample of chimpanzees. We then plotted data from all of the taxa in this space to examine phyletic variation in neural organization. Most of the variance in mountain gorillas, as well as other great apes, was contained within the chimpanzee range along the first two PCs, which accounted for 61.73% of the total variance. Thus, the majority of interspecific variation in brain structure observed among these ape taxa was no greater than the within-species variation seen in chimpanzees. The loadings on PCs indicated that the brain structure of great apes differs among taxa mostly in the relative sizes of the striatum, cerebellum, and hippocampus. These findings suggest possible functional differences among taxa in terms of neural adaptations for ecological and locomotor capacities. Importantly, these results fill a critical gap in current knowledge regarding great ape neuroanatomical diversity.

Animals↗

PubMed2006

Reciprocation and interchange in wild Japanese macaques: grooming, cofeeding, and agonistic support.

Social primates spend a significant proportion of their time exchanging grooming with their group companions. Although grooming is mainly exchanged in kind, given its hygienic and tension-reducing functions, it is still debated whether grooming also provides some social benefits, such as preferential access to resources (e.g., food or mating partners). In this study we analyzed grooming distribution among wild female Japanese macaques living in two groups on Yakushima. We tested the tendency of monkeys to reciprocate the amount of grooming received, and to direct their grooming up the hierarchy. Then we analyzed the relation of grooming to three of its possible benefits: reduced aggression, increased tolerance over food, and agonistic support against a male aggressor. The data were analyzed by means of row-wise matrix correlations. Grooming was highly reciprocated (i.e., exchanged in kind) and directed up the hierarchy in both the study groups. No significant relationship was found between grooming and aggression. Conversely, grooming favored tolerance over food, since it was positively correlated with presence on the same food patch, close proximity, and close approaches (both within 1 m) during feeding. Grooming was also positively related to agonistic support against adult males, although this relationship became nonsignificant when we controlled for kinship. Although these results are not definitive, they suggest that monkeys may derive various social benefits from grooming. This conclusion is supported by the fact that in various primate species animals tend to prefer high-ranking individuals as grooming partners.

Aggression↗

PubMed1980

Components of racial variation in finger ridge-counts.

Principal components analysis was used to evaluate finger ridge-count variability as an indicator of genetic relationships between populations. The analysis was carried out on American White, American Black and African Black samples, each including both sexes. Each individual is represented as a vecotr of 20 counts, a radial and an ulnar count for each digit. No assumptions were made prior to analysis concerning the number of meaningful components, and all were examined sequentially. The first five eigenvectors extracted from the within-groups correlation matrix have loadings very similar to those previously described by Roberts and Coope ('75). However, it is the component scores derived from the sixth eigenvector which show the most marked variation, accounting for 45% or more of the D2 in all Black-White comparisons. A number of other components also show significant intergroup heterogeneity, but they often do not accord with what is known of the genetic relationships between the populations. Apparently a large amount of ridge-count variation is not genetically meaningful, at least as far as these populations are concerned.

Africa, Western↗

PubMed1981

A multivariate analysis of temporal change in Arikara craniometrics: a methodological approach.

We have examined temporal changes in the cranial architecture of Arikara Amerindians from five archaeological sites in South Dakota which span a time period of approximately 230 years (ca. A.D. 1600-1830). We have utilized a multivariate statistical method based on a principal components analysis of the pooled within-groups correlation matrix rather than the more traditional methods of ascertaining morphological relationships, e.g., discriminant functions, Mahalanobis' D2, or Penrose's Size and Shape. Our component structure, based on a regional sample and the mathematically simpler principal components analysis, is very similar to the factor structure obtained by Howells (1973) using a world-wide sample and factor analysis proper. This supports the notion of the "universality" of cranial structure. An axis of temporal variation was introduced into the component space by means of multiple regression. This analysis indicates that a substantial portion of the intergroup variation is temporal in nature and the systematic temporal changes occur along the facial height, transverse frontal flatness, and frontal profile flatness components. Earlier analyses of the same material by more conventional methods either did not detect the temporal trends at all or failed to isolate the specific nature of the temporal changes. The success of the present analysis attests to the value of examining morphological relationships be means of principal components.

Cephalometry↗

PubMed1989

Spatial patterns of human gene frequencies in Europe.

The aims of this study of spatial patterns of human gene frequencies in Europe are twofold. One is to present new methodology developed for the analysis of such data. The other is to report on the diversity of spatial patterns observed in Europe and their interpretation as evidence of population processes. Spatial variation in 59 allele and haplotype frequencies (26 genetic systems) for polymorphisms in blood antigens, enzymes, and proteins is analyzed for an aggregate of 3,384 localities, using homogeneity tests, one-dimensional and directional spatial correlograms, and SYMAP interpolated surfaces. The data matrices are reduced to reveal the principal patterns by clustering techniques. The findings of this study can be summarized as follows: 1) There is significant heterogeneity in allele frequencies among the localities for all but one genetic system. 2) There are significant spatial patterns for most allele frequencies. 3) There is a substantial minority of clinal patterns in these populations. Clinal trends are found more frequently in HLA alleles than for other variables. North-south and northwest-southwest gradients predominate. 4) There is a strong decline in overall genetic similarity with geographic distance for most variables. 5) There are few, if any, appreciable correlations in pairs of allele frequencies over the continent, and there is little interesting correlation structure in the resulting correlation matrix. 6) Few spatial correlograms are markedly similar to each other, yet they form well-defined clusters. Spatial variation patterns, therefore, differ among allele frequencies. Patterns of human gene frequencies in modern Europe are diverse and complex. No single model suffices for interpretation of the observed genetic structure. Some clinal patterns reported here support the Neolithic demic-expansion hypothesis, others suggest latitudinal selection. Most of the clinal patterns are in HLA alleles, but there is also evidence from ABO for east-west migration diffusion. The majority of patterns are patchy, consistent with hypotheses of isolation by distance or of settlement of genetically differing, subsequently expanding ethnic groups. While undoubtedly there has been an ongoing stochastic process of differentiation consistent with the isolation-by-distance model, this has not obscured the directional patterns caused by migration (demic diffusion), and has perhaps only reinforced the contribution from settlement of ethnic units to patterns of genetic variation. However, the impact of the latter is most difficult to discern and requires further methodological developments.

ABO Blood-Group System↗

PubMed2005

Craniometric variation and population history of the prehistoric Tewa.

Although the population history and social organization of the prehistoric Pueblo Indians of the American Southwest have received attention in the archaeological literature, little research on this topic has been conducted by biological anthropologists. Here, we examine postmarital residence at two ancestral Tewa Indian pueblos located in north-central New Mexico using determinant ratio analysis. In addition, we examine genetic relationships among pueblos, as well as levels of within-pueblo heterogeneity due to gene flow from extraregional sources, or regional aggregation. Results from determinant ratio analysis indicate greater within-pueblo male variation, consistent with matrilocal residence for at least one Tewa pueblo. Less than expected heterogeneity at two pueblos suggests that endogamy might have been practiced among some prehistoric Tewa pueblos. Gene flow from extraregional sources is indicated for two different pueblos by greater than expected within-group heterogeneity. Distance matrix correlation analyses indicate little if any relationship between phenotypic and geographic distances, suggesting that geography was not the primary basis of gene flow or mate exchange. The weak relationship between phenotypic and geographic distances may be the combined effects of endogamy at some pueblos, nonrandom extraregional gene flow or migration at other pueblos, and limited nonproximity-dependent regional gene flow or migration among pueblos, possibly structured on ritual exchange networks based on medicine society affiliation.

Anthropology↗

PubMed2003

Candidate-gene association studies with pedigree data: controlling for environmental covariates.

Case-control studies provide an important epidemiological tool to evaluate candidate genes. There are many different study designs available. We focus on a more recently proposed design, which we call a multiplex case-control (MCC) design. This design compares allele frequencies between related cases, each of whom are sampled from multiplex families, and unrelated controls. Since within-family genotype correlations will exist, statistical methods will need to take this into account. Moreover, there is a need to develop methods to simultaneously control for potential confounders in the analysis. Generalized estimating equations (GEE) are one approach to analyze this type of data; however, this approach can have singularity problems when estimating the correlation matrix. To allow for modeling of other covariates, we extend our previously developed method to a more general model-based approach. Our proposed methods use the score statistic, derived from a composite likelihood. We propose three different approaches to estimate the variance of this statistic. Under random ascertainment of pedigrees, score tests have correct type I error rates; however, pedigrees are not randomly ascertained. Thus, through simulations, we test the validity and power of the score tests under different ascertainment schemes, and an illustration of our methods, applied to data from a prostate cancer study, is presented. We find that our robust score statistic has estimated type I error rates within the expected range for all situations we considered whereas the other two statistics have inflated type I error rates under nonrandom ascertainment schemes. We also find GEE to fail at least 5% of the time for each simulation configuration; at times, the failure rate reaches above 80%. In summary, our robust method may be the only current regression analysis method available for MCC data.

Case-Control Studies↗

PubMed2001

Comparison of three methods for obtaining principal components from family data in genetic analysis of complex disease.

Three multivariate techniques used to derive principal components (PCs) from family data were compared for their ability to model family data and power to detect linkage. Using the simulated data from Genetic Analysis Workshop 12, the five quantitative traits were first adjusted for age, sex, and environmental factors 1 and 2. Then, standard PCs, PCs obtained from between-family covariance, and PCs obtained from within-family genetic covariance were derived and subjected to multivariate sib pair linkage analysis. The standard PCs obtained from the overall correlation matrix allowed identification of key features of the true genetic model more readily than did the other methods. For detection of linkage, standard PCs and PCs obtained from the between-family genetic covariance performed similarly in terms of both power and type 1 error, and both methods performed better than the PCs obtained from within-family genetic covariance.

Chromosome Mapping↗

PubMed2004

Frequent compartmentalization of hepatitis C virus variants in circulating B cells and monocytes.

Differences in the composition of the hepatitis C virus (HCV) quasispecies between plasma and blood mononuclear cells (BMC) strongly suggest that BMCs support viral replication. We examined the frequency of such compartmentalization, the cell types involved, the constraints exerted on the different variants, and the role of immunoglobulin-complexed variants. We screened the hypervariable region (HVR1) of HCV isolates from 14 HBsAg- and HIV-seronegative patients with chronic HCV infection. HCV RNA was amplified and cloned from plasma, the immunoglobulin G (IgG)-bound fraction, and total and sorted BMCs (CD19+, CD8+, CD4+, and CD14+ cells). Compartmentalization was estimated using a matrix correlation test. The ratio of nonsynonymous/synonymous substitutions (d(N)/d(S) ratio) was calculated for each compartment. HCV RNA was detected in 3/3 BMC, 11/11 CD19+, 10/11 CD14+, 4/11 CD8+ and 0/11 CD4+ cell samples. HVR1 sequences were significantly different between plasma and at least one cellular compartment in all nine cases analyzed, and between B cells (CD19+) and monocytes (CD14+) in all five available cases. IgG-bound variants were distinct from cellular variants. D(N)/d(S) ratios were similar (n = 3) or lower (n = 6) in cellular compartments compared with plasma and the IgG-bound fraction. In conclusion, HCV compartmentalization is a common phenomenon. B cells and monocytes harbor HCV variants showing a low rate of nonsynonymous mutations, a feature that might contribute to the persistence of HCV infection.

Adult↗

PubMedDate not supplied

The relationship between caregiver burden and TBI survivors' cognition and functional ability after discharge.

This exploratory correlational clinical study examines the relationship between reported caregiver burden (as measured by the Burden Interview) and cognition and functional ability (as measured by the Functional Independence Measure instrument) of people who had experienced traumatic brain injury (TBI). The purpose of the research was to explore the impact of cognition and functional ability in adults with TBI on perceived caregiver burden. Forty-two subjects with TBI and their caregivers were studied during the follow-up clinic appointment 3 months after discharge from a 31-bed inpatient rehabilitation unit. Demographic data and relationships to previous studies were explored. Pearson correlation matrixes and a simple single regression model were used to examine the relationships. Functional ability and cognition both negatively affected reported caregiver burden, although the relationship was not statistically significant.

Activities of Daily Living↗

PubMed1994

Comparison of radiographic absorptiometry with dual-energy x-ray absorptiometry and quantitative computed tomography in normal older white and black women.

Bone mineral density (BMD) of the phalanges of the hand was measured by the technique of radiographic absorptiometry (RA) in 199 older postmenopausal women previously determined to have normal BMD by dual-energy x-ray absorptiometry (DXA) and quantitative computed tomography (QCT). The average age of the women was 66.8 +/- 4.9 years, and they were 19.9 +/- 6.7 years postmenopause. In the 54 black women, phalangeal BMD was 11.7% greater than in the 145 white women, a difference comparable to that found using DXA at the radial midshaft, the lumbar spine, and femoral neck. A correlation matrix comparing BMD measured by RA to BMD measured by DXA and QCT indicates that, in general, RA was related to the various DXA and QCT measurement sites as well as these sites were related to each other. When results for RA, DXA, and QCT obtained in our cohort of older women were compared to available reference data for peak adult bone mass, the average difference (SD units) from peak value was greatest for RA (-1.77 radius, -1.24 spine, -2.13 femoral neck, -2.34 QCT spine, and -2.71 phalanges). We conclude that RA is an acceptable measure of phalangeal BMD and that the data in our cohort can serve as reference data for older white and black women aged 55-75 years. Once the ability of RA to predict future fracture occurrence has been demonstrated, it could be rapidly deployed as a low-cost, widely available bone mass measurement technique.

Absorptiometry, Photon↗