Barry I- Graubard and Edward L. Korn
Barry I. Graubard and Edward L. Korn
The scatterplot is one of the most useful graphical displays of bivariate data. It allows one to see general trends and atypical points simultaneously, as well as other aspects of the data. A second feature of survey data is that some of it may be imputed to account for item non-response. A third feature is that the sample sizes can be large. A fourth feature is that the observations may have intraclass correlation due to cluster sampling. Survey designs typically specify that individuals are to be sampled with unequal probabilities of selection. The sample weight associated with an individual is the inverse of that individual's probability of being included in the sample, adjusted, if necessary, for non-response. For some applications, it may be useful to sample points for a sampled scatterplot not just proportionally to the sample weights. More direct approaches to estimating smooth conditional percentile or mean curves are possible using the original ungrouped data.
J. H.S. Blaxter
This chapter focuses on the species of Krill. It discusses the body form of the species and marked variations that were revealed during studies by various experts. The body form of a species can often vary, in some cases quite markedly. Mauchline and Fisher refer to the descriptions of forms of Thysanoessa inermis, Nematoscelis dificitis, Stylocheiron affine, and S. longicorne. Reference is also made to the smaller degrees of variation and to sexual dimorphism found among the following species: Euphausia diomedeae, E. triacantha, E. similis, E. vallentini, Nematoscelis microps, N. atlantica, and N. tenella. New forms of species have been described and further accounts of variation within species are now available. The chapter describes the similar as well as varied features between a male and a female krill and elaborates on the key identifiers between them. It also briefly discusses the key anatomic aspects of the species and traces the path of its evolution.