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At least 847 records · Page 47Linked to original sources
PubMed1989

Sample size and statistical power in the hierarchical analysis of variance: applications in morphometry of the nervous system.

Analysis of variance is commonly used in morphometry in order to ascertain differences in parameters between several populations. Failure to detect significant differences between populations (type II error) may be due to suboptimal sampling and lead to erroneous conclusions; the concept of statistical power allows one to avoid such failures by means of an adequate sampling. Several examples are given in the morphometry of the nervous system, showing the use of the power of a hierarchical analysis of variance test for the choice of appropriate sample and subsample sizes. In the first case chosen, neuronal densities in the human visual cortex, we find the number of observations to be of little effect. For dendritic spine densities in the visual cortex of mice and humans, the effect is somewhat larger. A substantial effect is shown in our last example, dendritic segmental lengths in monkey lateral geniculate nucleus. It is in the nature of the hierarchical model that sample size is always more important than subsample size. The relative weight to be attributed to subsample size thus depends on the relative magnitude of the between observations variance compared to the between individuals variance.

Aging↗
PubMed2006

Additive partitioning of rarefaction curves and species-area relationships: unifying alpha-, beta- and gamma-diversity with sample size and habitat area.

Additive partitioning of species diversity is widely applicable to different kinds of sampling regimes at multiple spatial and temporal scales. In additive partitioning, the diversity within and among samples (alpha and beta) is expressed in the same units of species richness, thus allowing direct comparison of alpha and beta. Despite its broad applicability, there are few demonstrated linkages between additive partitioning and other approaches to analysing diversity. Here, we establish several connections between diversity partitions and patterns of habitat occupancy, rarefaction, and species-area relationships. We show that observed partitions of species richness are equivalent to sample-based rarefaction curves, and expected partitions from randomization tests are approximately equivalent to individual-based rarefaction. Additive partitions can also be applied to species-area relationships to determine the relative contributions of factors influencing the beta-diversity among habitat fragments.

Animals↗
PubMed1991

Disposable endoscopic biopsy forceps: comparison with standard forceps of sample size and adequacy of specimen.

Disposable biopsy forceps have recently been introduced into the field of endoscopy. We have analyzed biopsy size and histologic interpretation of samples obtained with the disposable forceps and compared them to those obtained with reusable forceps. In the 18 patients studied, 49 samples were collected with the reusable forceps and 47 samples with the disposable. Biopsy sites included the colorectum in 50%, esophagus in 22%, small bowel in 17%, and stomach in 11% of the patients. We found that statistically smaller samples were collected by the disposable biopsy forceps than by the reusable (2.48 +/- 1.11 mm versus 1.99 +/- 0.55 mm, p = 0.006). The smaller biopsy size with disposable forceps was not clinically important since all but one of 47 specimens were interpreted as adequate for histologic diagnosis. The convenience, potential cost savings, and prevention of the spread of communicable agents afforded by disposable biopsy forceps make them a possible alternative to conventional forceps in some clinical settings.

Adult↗
PubMed2003

The distribution of water in degrading polyglycolide. Part I: sample size and drug release.

The effect of sample thickness on the degradation of polyglycolide (PGA) disks and on their drug release profiles is explored in this paper, and conclusions drawn about the distribution of water across a sample during degradation. The degradation process was monitored by measuring changes in the long period calculated from small angle X-ray scattering profiles, and by following changes in the pH of the buffer solutions. Drug release profiles were obtained using UV-spectrophotometry. The measurements suggest that reaction-erosion fronts form at the surface of all samples after around 7 days of degradation, and that these fronts progress through the sample at a constant rate of 0.032 mm/day. The data are consistent with a model in which drug is released quickly from the porous, hydrated regions behind the front, and reaches 100% release when the fronts meet.

Journal Article↗