Simple pooling

This phenomenon, known as Simpson s Paradox, illustrates the dangers of simple pooling. A meta-analysis for the data in the example would be based on the separate tables and compute a treatment difference for those patients with small stones and a treatment difference for patients with larger stones. These two differences would then be averaged to give a valid combined treatment difference. 

Needham, D. J. and Merkin, J. H. (1989). Pattern formation through reaction and diffusion in a simple pooled-chemical system. Dyn. Stab. Sysi., 3,... 

Pooling experiments are of two basic types, simple or orthogonal. In simple pooling, each individual appears in exactly one pool see Figure 1(a), where each circle in the box represents an individual, and individuals in the same column are in the same pool. An active pool response must be followed by individual testing to determine which specific individuals in the pool are active. In orthogonal pooling... 

Figure 1. (a) Simple pooling Individuals, represented by circles, are pooled according to their column location each individual appears in exactly one pool, (b) Two-way orthogonal pooling Individuals are pooled according to both their column and row locations each individual appears in exactly two pools. 

The mechanism of fluorescein staining of ocular epithelia has been subject to some conjecture. In earlier work it was suggested that staining occurred due to accumulation in intraepithelial spaces rather than direct staining of the cells. However, it has become clear that fluorescein can directly stain diseased human corneal cells and rabbit epithelial cells. Moreover, the hyperfluorescence that probably represents micropunctate clinical staining is likely due to optimum dye concentration and fluorescence within the cell rather than simple pooling. Cellular hyperfluorescence occurred from both mechanical abrasion and chemically induced toxicity, conditions that presumably promote an intracellular concentration that allows definitive clinical visualization. An issue that has received some attention is whether repeated... 

One of the first clues that lipid droplets were more than a simple pool of fat came in the early 1990s from research by Constantine Londos. He and his colleagues identified a protein called perilipin on the membrane of the lipid droplets in fat cells. They discovered that when cells are stimulated to metabolize the fatty acids in the lipid droplets, this protein is phosphorylated. This suggests a more complicated mechanism for controlling lipid digestion in fat cells than previously imagined. More than a half-dozen proteins have been identified on the membrane of lipid droplets. 

There are important statistical considerations in meta-analyses for the evaluation of safety. In particular, statistical methods must be valid in the presence of sparse data. As discussed previously, safety outcomes may be infrequent. Some trials may not have any relevant events. We refer to these trials as zero-event trials. The statistical methods should provide estimates with good bias properties and with valid standard errors and confidence intervals in the presence of low event coimts and zero-event trials. In any meta-analysis, the overall estimator and associated standard errors and confidence intervals should be stratified by the trials. Simple pooling of data across the trials can result in misleading results because of Simspon s paradox. With stratification, the randomize comparisons within trials are maintained. 

After an HWR NUE fuel bundle is discharged from the reactor, after about one year of irradiation, it is removed to a pool system for interim storage. The water in the pool removes the residual heat produced by the spent fuel and provides radiation shielding for workers. The compact design of the HWR fuel bimdle, and the impossibility of criticality for HWR natural uranium and low-enriched SEU spent fuel bundles under storage conditions in water pools (Frost 1994 Tsang et al. 1996) make for extremely simple pool storage. 

Merkin, J.H., Needham, D.J., Scott, S.K. On the creation, growth and extinction of oscillatory solutions for a simple pooled chemical reaction scheme. SIAM J. Appl. Math 47, 1040-1060 (1987)... 

The potential advantages of LPG concern essentially the environmental aspects. LPG s are simple mixtures of 3- and 4-carbon-atom hydrocarbons with few contaminants (very low sulfur content). LPG s contain no noxious additives such as lead and their exhaust emissions have little or no toxicity because aromatics are absent. This type of fuel also benefits often enough from a lower taxation. In spite of that, the use of LPG motor fuel remains static in France, if not on a slightly downward trend. There are several reasons for this situation little interest from automobile manufacturers, reluctance on the part of automobile customers, competition in the refining industry for other uses of and fractions, (alkylation, etherification, direct addition into the gasoline pool). However, in 1993 this subject seems to have received more interest (Hublin et al., 1993). 

The measurement of fluorescence intensity from a compound containing cliromophores of two spectral types is an example of a system for which it is reasonable to operate witli tire average rates of energy transfer between spectral pools of molecules. Let us consider tire simple case of two spectral pools of donor and acceptor molecules, as illustrated in figure C3.4.2 [18]. The average rate of energy transfer can be calculated as... 

A simple form of apparatus is that in which a cooled condensing surface is supported a few cm. above a shallow, heated pool of liquid, and the whole is enclosed in a highly evacuated chamber (compare Fig. II, 26, 1) this offers the least hindrance to the flow of vapour from the evaporating to the condensing surface. The rate of distillation is then determined by the rate at which the liquid surface is able to produce vapour. When the evaporating... 

In humans, vitamin B in phosphorylated forms is mostly unavaHable until hydrolyzed, then passively absorbed in the smaH intestine. The free vitamins are interconverted and suppHed to the ckculation by the Hver, then enter ceHs by simple diffusion and are phosphorylated. A typical adult pool of... 

FIG. 22-42 Four alternative modes of contimioiis-flow operation with a foam-fractionation column (1) The simple mode is illustrated hy the solid lines. (2) Enriching operation employs the dashed reflux line. (3) In stripping operation, the elevated dashed feed line to the foam replaces the solid feed line to the pool. (4) For combined operation, reflux and elevated feed to the foam are both employed. 

Operation m the Simple Mode if there is no concentration gradient within the liquid pool and if there is no coalescence within the rising foam, then the operation shown by the sohd hnes of Fig. 22-42 is truly in the simple mode, i.e., a single theoretical stage of separation. Equations (22-45) and (22-46) will then apply to the steady-flow operation. 

Results The uncertainties associated with the slopes are very different and n = H2, so that the pooled variance is roughly estimated as (V + V2)/2, see case c in Table 1.10 this gives a pooled standard deviation of 0.020 a simple r-test is performed to determine whether the slopes can be distinguished. (0.831 - 0.673)/0.020 = 7.9 is definitely larger than the critical /-value for p - 0.05 and / = 3 (3.182). Only a test for H[ t > tc makes sense, so a one-sided test must be used to estimate the probability of error, most likely of the order p = 0.001 or smaller. 

Their advantages are that they are simple to use and are transparent that is, the descriptors that best model the biological activity can be seen and— hopefully—understood. Their disadvantages are that they work best when restricted to congeneric series of compounds, they assume that the biological activity is a rectilinear function of each descriptor, and they can suffer from a high risk of chance correlations, especially when a large pool of descriptors is used. 

The basic principle underlying the development of images is simple (Lauterber, 1973). Consider a body cavity containing two pools of water in different quantities. In a uniform magnetic field, the NMR spectrum will consist of a single peak, since all the water molecules will process at the same frequency, irrespective of their spatial location. If, however, a linear field gradient is applied in the x -direction, the Larmor frequency of the water will increase linearly across the sample as a function of the x -coordinate, thereby creating a one-dimensional profile, or spectrum, of the sample (Fig. 7.21). 

OS 30] [R 30] [P 22] By simple flow switching, serial combinatorial synthesis for creating a cation pool from diverse carbamates and silyl enol ethers was accomplished (Figure 4.46) [66, 67]. The conversions and selectivities were comparable to continuous processing using three feed streams only (see Conversion/yield/selec-tivity, above). 

A simple two-dimensional example concerns the data from Table 33.1 and Fig. 33.9. The pooled variance-covariance matrix is obtained as [K K -1- L L]/(n, + 3 - 2), i.e. by first computing for each class the centred sum of squares (for the diagonal elements) and the cross-products between variables (for the other... 

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