Null Correlations Research Articles

Assessing the performance indices and design parameters of treatment wetlands for H +, Fe, and Mn retention

Using correlations analysis on water quality and wetland design parameters from a set of 35 natural wetlands receiving mine water, treatment efficiency was found to be a better index of Fe and Mn treatment than area-adjusted mass removal. However, area-adjusted mass removal was found to be a better index of performance for pH treatment. Weaknesses of using an area-adjusted measure to evaluate wetland performance for Fe retention included a significant load dependency aspect, strong positive correlations to inlet and outlet Fe concentrations, null correlations with vegetation parameters, and a tendency to rate highly small wetlands receiving high flow rates. H + retention was a better indication of pH treatment than treatment efficiency because of its relationships with inlet H + concentration, Fe treatment efficiency, and H + load. Design parameters enhancing Fe treatment efficiency included broad shapes, non-channelized flow patterns, high plant diversity, a southern exposure, and low Fe loads. Design parameters enhancing Mn treatment efficiency included large areas, non-channelized flow patterns, high vascular plant and bryophyte cover, high plant diversity, and low inlet Fe concentrations. Design parameters favoring pH mitigation included broad shapes, low flow rates, low surface water depths, non-channelized flow patterns, high plant diversity and cover, and low inlet Fe concentrations.

Factor analysis and the cerebral hemispheres: Pilot study and parietal functions

Although research on lateral differences has proliferated, attempts to specify fundamental dichotomies of hemispheric processing have yielded less than satisfactory results. The factor analysis of behavioral asymmetries can provide a different approach by helping to identify common functions underlying disparate tasks. It can also provide information on individual differences and interrelationships among functions. Here, the viability of the approach is demonstrated with a small pilot study ( N=29), and with two larger experiments ( N=70 and N=60) that stress parietal lobe function. Seven lateralized functions were identified: auditory lexical, spatial positional, spatial quantitative, tactile figural, visual emotional and visual lexical. A range of positive, negative and null correlations was found between functions, contrary to lateralization strength, hemisphericity, and independence models of individual differences in lateralization. However, a pattern of intercorrelations was observed among functions believed to be localized to the perisylvian region (Brodmann areas 22 and 39), which is consistent with the neurodevelopment theory of Geschwind and Galaburda ( Cerebral Lateralization Biological Mechanisms, Associations and Pathology, The MIT Press, Cambridge, MA, 1987).

Evolution à long terme des stratégies dans une tâche de comparaison phrase-dessin

Summary : Long term evolution of strategies in sentence-picture verification. Results of earlier experiments on subjects' cognitive processing during sentence-picture verification tasks indicate that spontaneous individual strategies are much more numerous and varied than the literature on this topic might suggest. To test the reliabilily of this finding, 13 subjects who had taken part in the original study were asked to participate one year later in the same sentence-picture verification task. Post-experintental verbal reports show that subjects retrieved their original strategy right from the outset of the experiment or after a few trials. Data analysis of processing times confirms verbatims. Regardless of the delay between two successive blocks of trials, or modification in instructions, the different subjects' individual mean processing times exhibit a stable pattern : sentence processing time and picture processing time form two distinct groups of variables where correlation is high; in contrast the low or null correlations across these two sets of processing times suggest they may be considered as independent. Key words : sentence-picture verification, strategies, individual differences.

A new approach to null correlations of proportions

Much work on the statistical analysis of compositional data has concentrated on the difficulty of interpreting correlations between proportions with an assortment of tests for nullcorrelations, for independence except for the constraint, F-independence of bounded variables, neutrality in the mean and in the median. This paper questions the appropriateness of characterizing the dependence structure of proportions in terms of such concepts, suggests an alternative method of modeling, develops necessary distribution theory and tests, and illustrates the methodology in applications.

Minres factor analysis of hypersthene data, Strathcona Mine (Ontario, Canada)

This is the first application of minimum residuals (minres),a type of factor analysis, in the study of hypersthene minerals from a mafic norite formation at the Strathcona Mine near Sudbury, Ontario. Minres, because it yields highest communalities for some variables, is preferred to other types of factoring solutions including a common factor model with Chayes' null correlations as factor input. Oblique rotation of factors is rejected as a model for statistical and geochemical reasons. A five oxide-variable model that reasonably well determines hypersthene is reduced by minres to a two-factor model which is statistically significant. Because of the small number of variables in the analysis, it is difficult to interpret the isolated factors in terms of specific geologic processes. The factors, however, even if surrogate, are linked with substitution phenomena in the hypersthene.

Note on Closure Correlation

Given a matrix of product-moment correlation coefficients computed on 'closed data' (a system of percentage variables), the test of departure from zero correlation is clearly inappropriate because closure of data imposes non-zero correlation.Subroutine CHAYES estimates 'Null Correlations' and calculates a t-matrix which may be used to test the hypothesis that observed product-moment correlations are due to the closure property. The calculated t-matrix is at best an approximation. This is found in certain mathematical assumptions leading to this t-test, and the recognition that statistical assumptions in the theory of t-testing are not satisfied. Great care must be exercized in accepting or rejecting correlations by this test. Therefore, results of the t-test are no substitute for sound geological reasoning, caveat emptor.