Elucidating the Foundations of Statistical Inference with 2 x 2 Tables

To many, the foundations of statistical inference are cryptic and irrelevant to routine statistical practice. The analysis of 2 x 2 contingency tables, omnipresent in the scientific literature, is a case in point. Fisher''s exact test is routinely used even though it has been fraught with controversy for over 70 years. The problem, not widely acknowledged, is that several different p-values can be associated with a single table, making scientific inference inconsistent. The root cause of this controversy lies in the table''s origins and the manner in which nuisance parameters are eliminated. However, fundamental statistical principles (e.g., sufficiency, ancillarity, conditionality, and likelihood) can shed light on the controversy and guide our approach in using this test. In this paper, we use these fundamental principles to show how much information is lost when the tables origins are ignored and when various approaches are used to eliminate unknown nuisance parameters. We present novel likelihood contours to aid in the visualization of information loss and show that the information loss is often virtually non-existent. We find that problems arising from the discreteness of the sample space are exacerbated by p-value-based inference. Accordingly, methods that are less sensitive to this discreteness - likelihood ratios, posterior probabilities and mid-p-values - lead to more consistent inferences.     

Lateral reorganization of plasma membrane is involved in the yeast resistance to severe dehydration

In this study, we investigated the kinetic and the magnitude of dehydrations on yeast plasma membrane (PM) modifications because this parameter is crucial to cell survival. Functional (permeability) and structural (morphology, ultrastructure, and distribution of the protein Sur7-GFP contained in sterol-rich membrane microdomains) PM modifications were investigated by confocal and electron microscopy after progressive (non-lethal) and rapid (lethal) hyperosmotic perturbations. Rapid cell dehydration induced the formation of many PM invaginations followed by membrane internalization of low sterol content PM regions with time. Permeabilization of the plasma membrane occurred during the rehydration stage because of inadequacies in the membrane surface and led to cell death. Progressive dehydration conducted to the formation of some big PM pleats without membrane internalization. It also led to the modification of the distribution of the Sur7-GFP microdomains, suggesting that a lateral rearrangement of membrane components occurred. This event is a function of time and is involved in the particular deformations of the PM during a progressive perturbation. The maintenance of the repartition of the microdomains during rapid perturbations consolidates this assumption. These findings highlight that the perturbation kinetic influences the evolution of the PM organization and indicate the crucial role of PM lateral reorganization in cell survival to hydric perturbations.     

7H-Pyridocarbazole, a Probe to Study the Role of Diphosphatidylglycerol in the Functioning of the Cytochrome Oxidase Complex of Mitochondria

Ditercalinium, the generic name for 7H-pyridocarbazole dimer,is a planar aromatic cation which exhibits strong inhibitoryeffects on the respiratory chain of plant mitochondria. By enzymaticassays and spectroscopic studies, the inhibition is shown tooccur at the level of the cytochrome c oxidase complex. It issuggested that the mechanism of inhibition could be due to thecomplexation of the aromatic cation with the diphosphatidylglycerolenvironment essential for cytochrome c oxidase activity ratherthan to a drug-enzyme direct interaction. 7H-pyridocar-bazolecan be used as an appropriate tool to study the role that negativelycharged acidic phospholipids, as diphosphatidylglycerol, playin the functioning of cytochrome c oxidase. (Received July 10, 1989; Accepted February 19, 1990)     

Concentrations and characteristics of procyanidins and other phenolics in apples during fruit growth

Apples (Malus domestica Borkh.) of two table and two cider cultivars were collected during fruit growth and maturation from the end of cell proliferation. Concentrations of flavonoids (flavan-3-ols, dihydrochalcones and flavonols) in the fruit flesh decreased sharply between circa 35 and circa 100 days after flowering. For hydroxycinnamic acids, the decrease appeared slower. In a second experiments apples of the cider cultivars Kermerrien and Avrolles were sampled every 2 weeks from 40 days after flowering to overripeness for a detailed characterisation of polyphenol accumulation kinetics in the fruit flesh. Most polyphenol synthesis had occurred at 40 days after full bloom, though it persisted at a low (Kermerrien) to very low (Avrolles) level during all the fruit growth. All qualitative characteristics of the polyphenols were remarkably stable. The degree of polymerisation of the procyanidins increased slightly in Avrolles and decreased in Kermerrien. This was accompanied by a relative increase in procyanidin B2, while size-exclusion chromatography of Kermerrien polyphenol extracts showed the disappearance of a highly polymerised fraction.     

Kinetic modelling of steam gasification of various woody biomass chars: influence of inorganic elements

A study was performed on the influence of wood variability on char steam gasification kinetics. Isothermal experiments were carried out in a thermobalance in chemical regime on various wood chars produced under the same conditions. The samples exhibited large differences of average reaction rate. These differences were linked neither with the biomass species nor age and may be related to the biomass inorganic elements. A modelling approach was developed to give a quantitative insight to these observations. The grain model was used on one biomass of reference for temperatures between 750 and 900 °C and steam partial pressures between 0 and 0.27 bar. The model was applied to the other samples through the addition of an integral parameter specific to each sample. A satisfactory correlation was found between this parameter and the ratio potassium/silicium. This result highlighted the catalytic effect of potassium and inhibitor effect of silicium on the reaction.