Power, sample size, experimental design

FIGURE 11.23 Power analysis.The desired difference is >2 standard deviation units (X, - / = 8). The sample distribution in panel a is wide and only 67% of the distribution values are > 8. Therefore, with an experimental design that yields the sample distribution shown in panel a will have a power of 67% to attain the desired endpoint. In contrast, the sample distribution shown in panel b is much less broad and 97% of the area under the distribution curve is >8. Therefore, an experimental design yielding the sample distribution shown in panel B will gave a much higher power (97%) to attain the desired end point. One way to decrease the broadness of sample distributions is to increase the sample size. 

A randomized crossover design has theoretical appeal because it eliminates the largest source of experimental variance interindividual variability. This could significantly enhance statistical power and permit much smaller samples sizes to detect a treatment effect. Unfortunately, a crossover design is appropriate only in rare cases in psychopharmacology, namely in studies ... 

The power of the statistical test is a quantitative measure of the ability to differentiate accurately differences in populations. The usual case in toxicity testing is the comparison of a treatment group to control group. Depending on the expected variability of the data and the confidence level chosen, an enormous sample size or number of replicates may be required to achieve the necessary discrimination. If the sample size or replication is too large, then the experimental design may have to be altered. 

Mclndoe, J.X. She, Microarray experimental design power and sample size considerations, Physiol. Genomics 2003, 16, 24-28. 

Page, G. P., et al. (2006). The PowerAtlas a power and sample size atlas for microarray experimental design... 

The independent comparative testing of the experimental samples of the internally-made power sources of IGIC 1142 size and the Toshiba s L43 (both size designations stand for similar cell sizes) were carried out. It was shown that power sources containing manganese dioxide cathode obtained... 

Jimenez et al. also used the ICP-MS method for the determination of Al, Ba, Bi, Cd, Co, Cu, Mn, Ni, Pb, Sn, and V. The main differences that they initiated focused on the on-line formation of olive oil-in-water emulsions, the considerable time-gain, and the automatic sample preparation process. Among the various experimental parameters studied and optimized for the development of this method were emulsifier concentration at the mixing point, emulsifier concentration in the carrier solutions in the valves, injected sample emulsifier volumes, emulsion formation flow rate, design of the FIA manifold used (emulsion formation, reactor length, and size of the different connections), and the radiofrequency power in the plasma. 

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