Outcome selection bias in meta-analysis

Publication bias has been previously identified as a threat to the validity of a meta-analysis. Recently, new evidence has documented an additional threat to validity, the selective reporting of trial outcomes within published studies. Several diseases have several possible measures of outcome. Some articles might report only a selection of those outcomes, perhaps those with statistically significant results. In this article, we review this problem while addressing the questions: what is within-study selective reporting? how common is it? why is it done? how can it mislead? how can it be detected?, and finally, what is the solution? We recommend that both publication bias and selective reporting should be routinely investigated in systematic reviews.     

A sensitivity analysis for publication bias in systematic reviews

There is no simple method of correcting for publication bias in systematic reviews. We suggest a sensitivity analysis in which different patterns of selection bias can be tested against the fit to the funnel plot. Publication bias leads to lower values, and greater uncertainty, in treatment effect estimates. Two examples are discussed. An appendix lists the S-plus code needed for carrying out the analysis.     

The long-term role of organic amendments in building soil nutrient fertility: a meta-analysis and review

An exhaustive meta-analysis of 132 long-term (≥ 10 years) studies worldwide was carried out to determine the effects of the use of organic amendments (OA) and OA + inorganic fertiliser (IF) on soil nutrient fertility. The responses of (1) crop yield [over the whole duration of the period (yield_m) and at the end of the experiment (yield_f)], (2) soil organic carbon (OC), (3) size of microbial biomass, and (4) Olsen phosphorus (P) to OA and OA + IF compared with IF only (standard control) and no fertilisation (nil control) were investigated. The overall effect of OA alone on yield was significant when compared with the nil control, but not when compared with the standard control. Only when OA and IF were added to soils that met specific conditions (low initial fertility, sandy texture, near-neutral pH values, under tropical climate) they rendered a significantly greater yield_f than the corresponding standard controls. The continuous application of manure caused greater relative and absolute gains in soil OC than straw + IF but did not produce significant greater yields while causing a considerable increase in Olsen P over time. The use of OA and OA + IF increased the resilience of agronomic systems over that of IF alone, as inferred from the smaller coefficient of variation of crop yield over time. We conclude that while the use of OA along with IF provides some additional benefits on yields as compared with IF application alone (especially under the above-mentioned conditions), the selection of the OA type and application rate should be carefully considered in order to maximise the nutrient use efficiency and minimise any undesirable effects to the environment.     

Modelling the solubility in Bayer liquors: A critical review and new models

An accurate and tractable model of solubility is a pre-requisite for any careful study of precipitation. Reviewing the abundant literature on the sodium aluminate solutions and Bayer Liquor, the authors point out the need for a new model for the apparent solubility of aluminium in actual Bayer Liquors and propose such a model, based on the well established Wesolowski's expression for the infinite dilution solubility and extended Debye–Hückel expression including a large empirical b I term for the “activity coefficient effect”. They suggest a chemical interpretation for this feature.     

The effects of oral iron supplementation on cognition in older children and adults: a systematic review and meta-analysis

Background  

In observational studies anaemia and iron deficiency are associated with cognitive deficits, suggesting that iron supplementation may improve cognitive function. However, due to the potential for confounding by socio-economic status in observational studies, this needs to be verified in data from randomised controlled trials (RCTs).     

Influencing parameters in the electrochemical anodization of TiO2 nanotubes: Systematic review and meta-analysis

Comprehensive control of processing techniques is primordial when fine-tuning the morphological features of titanium dioxide nanotube arrays (TNTs). This systematic review and meta-analysis compiled articles published from 2007 to date on the synthesis and growth mechanism of nanotubes fabricated via electrochemical anodization and evaluated the potential relationships between anodizing conditions and the resulting structures. Studies were gathered from the Science Direct online database, screened according to predefined criteria, and evaluated for their eligibility. Ninety-nine studies were assessed in the meta-analysis, 87 of them on tube length, 80 on tube diameter, and 33 on wall thickness. Multiple linear regression was performed to test if anodization parameters significantly predicted the resulting morphology of TiO₂ nanotubular structures. Overall regression for the three responses was statistically significant (length: R² = 0.487, p < 0.001; diameter: R² = 0.899, p < 0.001; wall thickness: R² = 0.792, p < 0.001). Applied potential was one of the main effects predicting all three responses (p < 0.001 in every model). Other important main predictors were anodizing time for tube length (p < 0.001), water percentage for tube diameter (p < 0.001) and ammonium fluoride (NH₄F) concentration for wall thickness (p < 0.001).     

Modelling the flow in a hydrocyclone

A computational procedure is employed in the present work to predict the flow field in a hydrocyclone. Computations are carried out for turbulent flow under assumptions of axial symmetry. Turbulence closure has been affected with the help of the conventional k→ ? model that includes a new formulation of the turbulence dissipation equation. The existing formulation of the dissipation equation proved to be inadequate in predicting the true nature of the present flow field. Results of the procedure are discussed. The new model appears to predict correctly the behaviour of a conventional water-fed hydrocyclone in the absence of an air core.     

Reducing the effects of lead-time bias, length bias and over-detection in evaluating screening mammography: a censored bivariate data approach

Measuring the benefit of screening mammography is difficult due to lead-time bias, length bias and over-detection. We evaluated the benefit of screening mammography in reducing breast cancer mortality using observational data from the SEER-Medicare linked database. The conceptual model divided the disease duration into two phases: preclinical (T(0)) and symptomatic (T(1)) breast cancer. Censored information for the bivariate response vector ( T(0), T(1)) was observed and used to generate a likelihood function. However, the contribution to the likelihood function for some observations could not be calculated analytically, thus, censoring boundaries for these observations were modified. Inferences about the impact of screening mammography on breast cancer mortality were made based on maximum likelihood estimates derived from this likelihood function. Hazard ratios (95% confidence intervals) of 0.54 (0.48-0.61) and 0.33 (0.26- 0.42) for single and regular users (vs. non-users), respectively, demonstrated a protective effect of screening mammography among women 69 years and older. This method reduced the impact of lead-time bias, length bias and over-detection, which biased the estimated hazard ratios derived from standard survival models in favour of screening.     

Modelling transverse mixing in a rolling drum

In this paper, a new model of transverse mixing in a rotating drum is derived from dynamic data collected from an experimental rig. Since the active layer has often been declared as the zone that is responsible for the mixing of solids in a rolling bed, the active layer was characterized so that its properties could be predicted for a wide range of experimental conditions. The mixing model consisted of two correlations, one to predict the mixing rate in the drum and the other to predict the final contact between the two materials. These correlations were linked back to the operational variables of the drum, such as the drumfs loading, size and rotational velocity. By combining these two correlations the time required to fully mix the material in the drum could be predicted. The mixing model was tested against independent data and good agreement was observed between the experimentally derived results and those predicted by the mixing model. Furthermore, this mixing model was designed such that it would be easily applicable to different sized drums. The extrapolation ability was tested on different smaller‐sized drums and found to agree considerably with experimental results.     

Modelling a fish-hook in hydrocyclone selectivity curves

A dip or fish-hook in the fine end of the selectivity curve for hydrocyclones has been reported on several occasions. It is modelled by introducing an entrainment component to recovery to the underflow which is a function of particle size. Such entrainment is held to be physically reasonable.     

Modelling a continuous devulcanization in an extruder

An engineering kinetic model is applied to EPDM devulcanization in an extrusion process. Parameters that were included in the model are crosslink density, devulcanizing agent concentration, time, shear rate, and temperature. The extruder is considered as a series of plug flow and stirred tank reactors. The residence time is calculated using solid flow or liquid flow model, depending on the degree of decrosslinking. The model can accurately predict the decrosslinking degree inside the temperature boundary defined by the applied experimental conditions. Outside this boundary, the effect of chemical degradation on the measured conversion becomes more significant.     

Hydrocracking: a review

In this article the technology, kinetics, chemistry and reactor modelling of hydrocracking have been reviewed. While it is intended to provide a general overview of the recent advances in this process, greater emphasis has been given to technology and reactor modelling because of their industrial importance. Over ninety references have been cited.     

Modelling and control of different types of polymerization processes using neural networks technique: A review

Polymerization process can be classified as a nonlinear type process since it exhibits a dynamic behaviour throughout the process. Therefore, it is highly complicated to obtain an accurate mechanistic model from the nonlinear process. This predicament always been a “wall” to researchers to be able to devise an optimal process model and control scheme for such a system. Neural networks have succeeded the other modelling and control methods especially in coping with nonlinear process due to their very conciliate characteristics. These characteristics are further explained in this work. The predicament that is encountered by researchers nowadays is lack of data which consequently lead to an imprecise mechanistic model that scarcely conforms to the desired process. The implementations of the neural network model not only restrict to polymerization reactor but to other difficult‐to‐measure parameters such as polymer quality, polymer melts index and mixture of initiators. This work is aimed to manifest ascendancy of neural networks in modelling and control of polymerization process.     

Chain-extended polyethylene in context: a review

The subject of crystallization of polyethylene at high pressures, commonly known as chain-extended crystallization, is reviewed. An historical approach is taken for the topics of molecular conformation, the relationship to chain-folded growth and the responsibility of the hexagonal phase. With the identification of this new phase and the demonstration that chain-extended growth is crystallization of hexagonal polyethylene, the basis of understanding is established. The field is then surveyed in this new context with discussion of high pressure annealing and molecular mechanisms involved, implications for the understanding of kinetically controlled growth in general and the use of chain-extended polyethylene as a model for crystal growth and mechanical behaviour.     

PyMC: Bayesian Stochastic Modelling in Python

This user guide describes a Python package, PyMC, that allows users to efficiently code a probabilistic model and draw samples from its posterior distribution using Markov chain Monte Carlo techniques.     

Chronometric dating in archaeology: a review

Most archaeological dating methods are based on decay of a naturally occurring radioisotope. (14)C activity of fossil bones and charcoal decreases with age, but must be calibrated for past changes in atmospheric activity. Uranium absorbed by shells and stalagmites is used to date on a 10(5)-year scale by observing the decay of (234)U to (230) Th. Thermoluminescence, optical luminescence, and electron spin resonance detect trapped electronic charges generated by natural radioactivity in burned flint, beach sands, shells, and tooth enamel. Rate of racemization of amino acids in fossil shells is constant at constant T, and age can be tracked from an increase in the D/L ratio.     

Modelling endothermic reactions in a compound membrane reactor

This paper models the performance of a membrane reactor. The membrane, a composite alumina-based one, is packed with a catalyst and allows low molecular weight gases to diffuse through it at a faster rate than gases with a higher molecular weight. This allows a greater conversion to be achieved in one pass through the reactor. The reaction that is specifically considered in this paper is the dehydrogenation of methyl-cyclohexane to toluene with the production of hydrogen. This latter species is preferentially removed by the membrane. Data for the performance of the membrane have been estimated from previous experiments using single gases and the mechanisms considered are Knudsen and bulk flow. Surface flow is not considered in the model as it is possibly not important as the endothermic reaction is carried out at a high temperature. A standard kinetic model is also incorporated in the calculations. The correlations of maximum effective length of membrane reactors and maximum percentage conversion as functions of the feed velocity and the membrane diameter are demonstrated in this paper. This paper also considers the behaviour of a compound reactor in which the first section is a straightforward ‘plug flow’ reactor where the catalyst is confined in an impermeable tube with the same internal diameter as the membrane. This is followed by a section containing the membrane. The reason for considering this configuration is to avoid unnecessary leakage of methyl-cyclohexane feed in the initial stages of the reaction. This innovation leads to predicted increases in the overall conversion of the process.