Search results for "Statistical power"
showing 3 items of 23 documents
Overdispersion tests in count-data analysis.
2008
Count data are commonly assumed to have a Poisson distribution, especially when there is no diagnostic procedure for checking this assumption. However, count data rarely fit the restrictive assumptions of the Poisson distribution. The violation of much of such assumptions commonly results in overdispersion, which invalidates the Poisson distribution. Undetected overdispersion may entail important misleading inferences, so its detection is essential. In this study, different overdispersion diagnostic tests are evaluated through two simulation studies. In Exp. 1, the nominal error rate is compared under different sample sizes and Λ conditions. Analysis shows a remarkable performance of the χ…
On hidden heterogeneity in directional asymmetry – can systematic bias be avoided?
2006
8 pages; International audience; Directional asymmetry (DA) biases the analysis of fluctuating asymmetry (FA) mainly because among-individual differences in the predisposition for DA are difficult to detect. However, we argue that systematic bias mainly results from predictable associations between signed right-left asymmetry and other factors, i.e. from systematic variation in DA. We here demonstrate methods to test and correct for this, by analysing bilateral asymmetry in size and shape of an irregular sea urchin. Notably, in this model system, DA depended significantly on body length and geographic origin, although mean signed asymmetry (mean DA) was not significant in the sample as a wh…
Dimensional Latent Structure of Relationship Quality: Results of Three Representative Population Samples
2015
One central issue for every latent construct in psychology (e.g., relationship quality) is its latent nature: Differences in intelligence, for example, are traditionally considered to be dimensional (e.g., when quantifying intelligence by a standardized test score) rather than categorical (distinguishing different categories such as intelligent vs. unintelligent). When considering a categorical construct, such as Down syndrome, on the other hand, the characteristic is qualitative (groups are classified by existence or absence of an extra chromosome) rather than quantitative (varying degrees of Down syndrome). The group bound together by the possession of a certain characteristic (disease, d…