Dismantling the Mantel tests

The simple and partial Mantel tests are routinely used in many areas of evolutionary biology to assess the significance of the association between two or more matrices of distances relative to the same pairs of individuals or demes. Partial Mantel tests rather than simple Mantel tests are widely used to assess the relationship between two variables displaying some form of structure. We show that contrarily to a widely shared belief, partial Mantel tests are not valid in this case, and their bias remains close to that of the simple Mantel test. We confirm that strong biases are expected under a sampling design and spatial correlation parameter drawn from an actual study. The Mantel tests should not be used in case auto-correlation is suspected in both variables compared under the null hypothesis. We outline alternative strategies. The R code used for our computer simulations is distributed as supporting material

Adaptive Mantel Test for AssociationTesting in Imaging Genetics Data

Mantel's test (MT) for association is conducted by testing the linear relationship of similarity of all pairs of subjects between two observational domains. Motivated by applications to neuroimaging and genetics data, and following the succes of shrinkage and kernel methods for prediction with high-dimensional data, we here introduce the adaptive Mantel test as an extension of the MT. By utilizing kernels and penalized similarity measures, the adaptive Mantel test is able to achieve higher statistical power relative to the classical MT in many settings. Furthermore, the adaptive Mantel test is designed to simultaneously test over multiple similarity measures such that the correct type I error rate under the null hypothesis is maintained without the need to directly adjust the significance threshold for multiple testing. The performance of the adaptive Mantel test is evaluated on simulated data, and is used to investigate associations between genetics markers related to Alzheimer's Disease and heatlhy brain physiology with data from a working memory study of 350 college students from Beijing Normal University

Rolf Mantel and the Computability of General Equilibria: On the Origins of the Sonnenschein-Mantel-Debreu Theorem

In this brief paper we revise the original motivations of Rolf Mantel to pursue a proof of Sonnenschein´s conjecture. We contend that his work on computational models of general equilibrium lead him to seek an alternative to the usual fixed point theorems used in proofs of existence. Confronted with a paper of Uzawa and his own experience in programming a national planning system he found that the use of theorems like Brouwer´s and Kakutani´s was unavoidable. To check out whether Uzawa was right he sought to find out whether the only properties required of excess demand functions to ensure the existence of equilibria in competitive markets were continuity, homogeneity and Walras´ law. In 1974, he found that this was actually the case. We will see that this result and his interpretation were informed by Mantel´s interest in economic development and planning.Fil: Tohmé, Fernando

The Visible and the Invisible Hilary Mantel

This talk addresses the scarcity of critical material on Hilary Mantel’s writing in the academy. It questions the suitability of the ‘origin’ paradigm within the criticism that is available, which closes off the excess of Mantel’s texts through attempts to ‘unite’ her corpus. The ambiguity of her writing, and its suspicions, suggest Jacques Derrida’s thought as a pertinent means to read the differences in her work differently. The proximity of Jean-Luc Nancy’s philosophy with Derrida’s thought allows the significance of ellipsis to surface as a liberating catalyst for weaving the implications of Derrida’s thinking through the writing of Mantel. This synthesis constitutes an original combination because Mantel’s writing has not been closely studied, Derrida’s notion of ellipsis has been eclipsed by philosophy, and the combination of these two ‘invisibilities’ is seminal. The talk begins with an exploration of the mythologies I discovered and interrogated during the course of my thesis. It then considers the key points in Mantel’s writing career. In particular taking her from the difficulty and invisibility of 1979 when A Place of Greater Safety, her first novel, was rejected, to winning the Booker prize twice in succession in 2009 and 2012. It thereby traces the story of her shift from invisible to infamous, in terms of her treatment by the mainstream British media as well as her phenomenal post-millennium success.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

zt: A Sofware Tool for Simple and Partial Mantel Tests

Different methods of data analysis (e.g. clustering and ordination) are based on distance matrices. In some cases, researchers may wish to compare several distance matrices with one another in order to test a hypothesis concerning a possible relationship between these matrices. However, this is not always self-evident. Usually, values in distance matrices are, in some way, correlated and therefore the usual assumption of independence between objects is violated in the classical tests approach. Furthermore, often, spurious correlations can be observed when comparing two distances matrices. A classic example is the comparison between genetic and environmental distances. Colonies that are in close proximity of each other tend to have similar environments and therefore there will be a positive correlation between environmental and geographical distances. Such colonies will also be more likely to exchange migrants so that genetic distances will be positively correlated with spatial distances. The consequence is that an observed positive association between genetic and environmental distances may be simply due to spatial effects. The most widely used method to account for distance correlations is a procedure known as the Mantel test (Mantel,'67; Mantel and Valand,'70 following the pioneering work of Daniels,'44 ; Daniels and Kendall'47). The simple Mantel test considers two matrices while an extension known as the partial Mantel test considers three matrices. These tools are widely used in different fields of research such as population genetics, ecology, anthropology, psychometrics and sociology.

Friction Testing of a New Ligature

Objective: To determine if American Orthodontics\u27 (AO) new, experimental ligature demonstrates less friction in vitro when compared to four other ligatures on the market. Methods: Four brackets were mounted on a custom metal fixture allowing an 0.018-in stainless steel wire attached to an opposite fixture with one bracket to be passively centered in the bracket slot. The wire was ligated to the bracket using one of five types of ligatures including the low friction test ligatures (AO), conventional ligatures (AO), Sili–TiesTM, Silicone Infused Ties (GAC), Synergy® Low-Friction Ligatures (RMO), and SuperSlick ligatures (TP Orthodontics). Resistance to sliding was measured over a 7 mm sliding distance using a universal testing machine (Instron) with a 50 Newton load cell and a crosshead speed of 5 mm/min. The initial resistance to sliding (static) was determined by the peak force needed to initiate movement and the kinetic resistance to sliding was taken as the force at 5 mm of wire/bracket sliding. Fifteen unique tests were run for each ligature group in both dry and wet (saliva soaked for 24 hours with one drop prior to testing) conditions. Results: In the dry state, the SuperSlick ligature demonstrated more static friction than all of the other ligatures, while SuperSlick and Sili–Ties demonstrated more kinetic friction than the AO conventional, AO experimental and Synergy ligatures. In the wet condition, SuperSlick and the AO experimental ligature demonstrated the least static friction, followed by the AO conventional and Sili–Ties. The most static friction was observed with the Synergy ligatures. In the wet condition, the SuperSlick, AO experimental and AO conventional exhibited less kinetic friction than the Sili-Ties and Synergy ligatures. Conclusions: AO\u27s experimental ligature exhibits less friction in the wet state than conventional ligatures, Sili–Ties and Synergy and is comparable to the SuperSlick ligature. These preliminary results suggest that the AO experimental ligature and the SuperSlick ligature create less friction, but direct conclusions regarding in vivo performance cannot be made and randomized controlled clinical trials are needed to determine if these ligatures have clinical significance in treatment efficiency

The ecodist Package for Dissimilarity-based Analysis of Ecological Data

Ecologists are concerned with the relationships between species composition and environmental framework incorporating space explicitly is an extremely flexible tool for answering these questions. The R package ecodist brings together methods for working with dissimilarities, including some not available in other R packages. We present some of the features of ecodist, particularly simple and partial Mantel tests, and make recommendations for their effective use. Although the partial Mantel test is often used to account for the effects of space, the assumption of linearity greatly reduces its effectiveness for complex spatial patterns. We introduce a modification of the Mantel correlogram designed to overcome this restriction and allow consideration of complex nonlinear structures. This extension of the method allows the use of partial multivariate correlograms and tests of relationship between variables at different spatial scales. Some of the possibilities are demonstrated using both artificial data and data from an ongoing study of plant community composition in grazinglands of the northeastern United States.

Accounting for centre-effects in multicentre trials with a binary outcome – when, why, and how?

Open Access Research article Accounting for centre-effects in multicentre trials with a binary outcome – when, why, and how? Brennan C Kahan Correspondence: Brennan C Kahan [email protected] Author Affiliations Pragmatic Clinical Trials Unit, Queen Mary University of London, 58 Turner Street, London E1 2AB, UK MRC Clinical Trials Unit at UCL, 125 Kingsway, London WC2B 6NH, UK BMC Medical Research Methodology 2014, 14:20 doi:10.1186/1471-2288-14-20 The electronic version of this article is the complete one and can be found online at: http://www.biomedcentral.com/1471-2288/14/20 Received: 5 July 2013 Accepted: 3 February 2014 Published: 10 February 2014 © 2014 Kahan; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. Formula display: Abstract Background It is often desirable to account for centre-effects in the analysis of multicentre randomised trials, however it is unclear which analysis methods are best in trials with a binary outcome. Methods We compared the performance of four methods of analysis (fixed-effects models, random-effects models, generalised estimating equations (GEE), and Mantel-Haenszel) using a re-analysis of a previously reported randomised trial (MIST2) and a large simulation study. Results The re-analysis of MIST2 found that fixed-effects and Mantel-Haenszel led to many patients being dropped from the analysis due to over-stratification (up to 69% dropped for Mantel-Haenszel, and up to 33% dropped for fixed-effects). Conversely, random-effects and GEE included all patients in the analysis, however GEE did not reach convergence. Estimated treatment effects and p-values were highly variable across different analysis methods. The simulation study found that most methods of analysis performed well with a small number of centres. With a large number of centres, fixed-effects led to biased estimates and inflated type I error rates in many situations, and Mantel-Haenszel lost power compared to other analysis methods in some situations. Conversely, both random-effects and GEE gave nominal type I error rates and good power across all scenarios, and were usually as good as or better than either fixed-effects or Mantel-Haenszel. However, this was only true for GEEs with non-robust standard errors (SEs); using a robust ‘sandwich’ estimator led to inflated type I error rates across most scenarios. Conclusions With a small number of centres, we recommend the use of fixed-effects, random-effects, or GEE with non-robust SEs. Random-effects and GEE with non-robust SEs should be used with a moderate or large number of centres

Why do consumers pay bills electronically? an empirical analysis

Why do consumers use electronic bill payment services? what do the differences between nonusers, low users, and high users imply about the potential future market these services? How might public policy evolve in the future? Analyzing a unique consumer survey conducted by the Federal Reserve's Retail Product Office, the author finds important differences between nonusers, low users, and high users of electronic bill payment. The analysis suggests that the industry will need to address fundamental customer needs before a broader portion of consumers will adopt these services.Electronic funds transfers ; Payment systems ; Internet ; Electronic commerce