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Mediation analysis is widely used to test and inform theory and debate about the mechanism(s) by which causal effects operate, quantitatively operationalized as an indirect effect in a mediation model. Most effects operate through multiple mechanisms simultaneously, and a mediation model is likely to be more realistic when it is specified to capture multiple mechanisms at the same time with the inclusion of more than one mediator in the model. This also allows an investigator to compare indirect effects to each other. After an overview of the mechanics of mediation analysis, we advocate formally comparing indirect effects in models that include more than one mediator, focusing on the important distinction between questions and claims about value (i.e., are two indirect effects the same number?) versus magnitude (i.e., are two indirect effects equidistant from zero or the same in strength?). After discussing the shortcomings of the conventional method for comparing two indirect effects in a multiple mediator model—which only answers a question about magnitude in some circumstances—we introduce several methods that, unlike the conventional approach, always answer questions about difference in magnitude. We illustrate the use of these methods and provide code that implements them in popular software. We end by summarizing simulation findings and recommending which method(s) to prefer when comparing like- and opposite-signed indirect effects. [ABSTRACT FROM AUTHOR]

Guido Melchior's important and rich book (Melchior Knowing and Checking. An Epistemological Investigation2019) draws our attention to the much neglected topic of checking. There are many new leads to follow. Here, I will pick a few that seem to me to allow the most room for discussion and disagreement: the alleged modal profile of checking (Sect. 1), the contrastive aspects of checking (Sect. 2), and the relation of checking to closure (Sect. 3). I will end with two smaller points worth bringing up here (Sect. 4). [ABSTRACT FROM AUTHOR]

The aim of this paper is to determine whether and to what extent Woodward’s interventionist theory of causation is variable relative. In an influential review, Strevens has accused Woodward’s account of a damaging form of variable relativity, according to which obviously false causal claims can be made true by choosing a depleted variable set. Following McCain, I show that Strevens’ objection doesn’t succeed. However, Woodward also wants to avoid another kind of variable relativity, according to which it can be true that X is a cause of Y in one set of background conditions, but false in another. I show that Woodward’s account is problematically overpermissive, unless there are restrictions on the values that certain variables can take. I formulate a modified account that makes these restrictions explicit, then use it to argue that Woodward’s attempt to avoid relativity to background conditions is misguided. On the best interpretation of the interventionist theory, causal claims are assessed relative to a particular kind of variable set. Thus, I conclude that the theory should be understood as variable relative, in a specific, unproblematic sense. [ABSTRACT FROM AUTHOR]

We studied dependences of T2 relaxation time on magnetic field and concentration of nanoparticles. It was found that nanocontrast media are effective under the influence of the magnetic fields in the range 0.3-7 T. Data of electron paramagnetic resonance confirm the assumption on aggregation of nanoparticles not coated with proteins in high magnetic fields. [ABSTRACT FROM AUTHOR]

Effect size is a concept that can be especially useful in bioequivalence and studies designed to find important and not just statistically significant differences among responses to treatments based on independent random samples. We develop and explore a new effect size related to a maximal superiority ordering for assessing the separation among two or more normal distributions, possibly having different means and different variances. Confidence intervals and tests of hypothesis for this effect size are developed using a p value obtained by averaging over a distribution on variances. Since there is almost always some difference among treatments, instead of the usual hypothesis test of exactly no effect, researchers should consider testing that an appropriate effect size has at least, or at most, some meaningful magnitude, when one is available, possibly established using the framework developed here. A simulation study of type I error rate, power and interval length is presented. R-code for constructing the confidence intervals and carrying out the tests here can be downloaded from Author's website. [ABSTRACT FROM AUTHOR]

The mining of changes or differences or other comparative patterns from a pair of datasets is an interesting problem. This paper is focused on the mining of one type of comparative pattern called emerging patterns. Emerging patterns are denoted by EPs and are defined as patterns for which support increases from one dataset to the other with a big ratio. The number of EPs is sometimes huge. To provide a good structure for and to reduce the size of mining results, we use borders to concisely describe large collections of EPs in a lossless way. Such a border consists of only the minimal (under set inclusion) and the maximal EPs in the collection. We also present an algorithm for efficiently computing the borders of some desired EPs by manipulating the input borders only. Our experience with many datasets in the UCI Repository and recent cancer diagnosis datasets demonstrated that: Both the EP pattern type and our algorithm are useful for building accurate classifiers and useful for mining multifactor interactions, for example, minimal gene groups potentially responsible for the development of cancer. [ABSTRACT FROM AUTHOR]

A prospective study in 31 patients was designed to compare contrast quantitatively using axial conventional, gated spin-echo T2-weighted (T2W) (SE) (asymmetrical echo TE 30 and 80 ms) and axial dual-echo fast spin-echo (FSE) sequences (TE20 and 120 ms) to image lumbar discs, nerve roots, and cerebrospinal fluid CSF. We used two quantitative measures, percent (%) contrast and contrast-to-noise ratio (CNR), to compare the sequences. The FSE sequence had greater % contrast and CNR on the first and second echo images for both disc and nerve root detection using these scan parameters. An axial FSE sequence, therefore, provided contrast characteristics similar to those of gated axial T2W SE sequence in the lumbar spine, with a 60% saving in acquisition time. The FSE sequence is now our standard axial T2W study for the lumbar spine. [ABSTRACT FROM AUTHOR]

Statisticians often employ simultaneous confidence intervals to reduce the likelihood of their drawing false conclusions when they must make a number of comparisons. To do this properly, it is necessary to consider the family of comparisons over which simultaneous confidence must be assured. Sometimes it is not clear what family of comparisons is appropriate. We describe how computer software can monitor the types of contrasts a user examines, and select the smallest family of contrasts that is likely to be of interest. We also describe how to calculate simultaneous confidence intervals for these families using a hybrid of the Bonferroni and Scheffé methods. Our method is especially suitable for problems with discrete and continuous predictors. [ABSTRACT FROM AUTHOR]