SOME ISSUES IN THE DESIGN AND ANALYSIS OF SENSORY DATA: REVISITED

Sensory experimental data whether collected via the consumer or via the laboratory population have many characteristics in common. Among the more important characteristics are that they are relative, skewed, and difficult to replicate. These characteristics result from the use of human beings as instruments to measure multivariate stimuli as opposed to the use of a mechanical instrument. The use of human beings as instruments presents several problems in the design and analysis of sensory/consumer studies. In the clinical/medical applications of sensory evaluation, we have used people both as the experimental unit (panelists/subjects) and as the instrument (judges) to measure panelists’ responses. Thus it is my belief that sensory data are the most difficult scientific data to statistically analyze and interpret. Unfortunately, limited theoretical work has been done to tackle the resulting problems. These problems include the comparison of responses obtained from independent populations (monadic design), sample size estimation with special reference to time-dependent responses, analysis of degree of difference data, the invariance property of rating scales, effect of correlated errors in observations, and the use of laboratory panels to predict results from a consumer panel. Some solutions to these problems have been provided by experience. My purpose here is to discuss each of these problems in greater detail and offer some possible scientific solutions.     

MATHEMATICS OF A LADY TASTING TEA REVISITED

The British Standards Institution and the International Standards Organization specify that when mixtures of tea and milk are to be evaluated sensorially, the tea should be added to the milk. Four cups of tea prepared by pouring the tea into the cup first (TIF) and four cups prepared by placing the milk in the cup first (MIF) were presented to 155 panelists in the dark. They were instructed to select by taste the four cups containing the MIF tea. The frequency of correct selection was well above the chance level, indicating that the panelists had detected a difference in flavor. The same task was performed by 131 panelists except they evaluated the tea in light. The panelists were not highly trained tea tasters; in fact, most were not regular drinkers of hot tea. Notwithstanding that, their discriminating power was sufficient to resolve the subtle differences which did exist.     

CONFIDENCE LIMITS ON PHYLOGENIES: THE BOOTSTRAP REVISITED

Abstract— The bootstrap, a non-parametric statistical analysis, can be used to assess confidence limits on phylogcnics. The method most widely used tests the monophyly of individual clades. This paper proposes additional applications of the bootstrap which provide useful information about phylogeny even when many clades are found not to be supported with confidence (as often occurs in practice). In such cases it is still possible to place a constraint on the phylogenetic position of taxa by examining the relative size of the smallest monophyletic groups that contain them. In addition, the taxonomic composition of these larger clades can be determined, as well as the relative likelihood of their occurrence. The distinction between hypotheses about membership in particular clades and hypotheses about entire topologies is also discussed. To investigate the latter, the bootstrap is used to estimate the sampling distribution of tree similarity indices. All methods are illustrated by reference to a large data set on the angiosperm family Asteraccae, selected from the literature.     

SPIRAL GROWTH: THE 'MUSEUM OF ALL SHELLS' REVISITED

Raup's model of shell growth, now in standard use, is operationalonly for strictly conispiral shells. The pertinence of evolutionaryinterpretations of the distribution of existing shells in themorphospace defined by Raup's parameters is questioned. A simple,more general model accounts for the non-isometric growth ofmany shells. Some aspects of the distribution of existing shellsin the morphospace derived from the new model are discussed. (Received 18 November 1996; accepted 11 March 1997)     

中长跑运动的心血管效应

本研究通过利用彩色多普勒超声心动图对２４例专业中长跑运动员的心脏形态、血液动力学改变及收缩舒张功能参数进行了观察,并与２０例从未参加过正规训练的同龄案牍工作者对照组进行了对比研究,结果显示：中长跑运动员的舒张末期左室内径（ＬＶＤｄ）、左室舒张末容量（ＬＶＥＤＶ）、收缩末容量（ＬＶＥＳＶ）、每搏量（ＳＶ）、左室心肌重量（ＬＶＭ）及左室心肌重量指数（ＬＶＭＩ）均高于对照组（Ｐ＜０．０１）;舒张早期峰值血流速度（ＰＦＶＥｃｍ／ｓ）高于对照组（Ｐ＜０．０１）;舒张晚期峰值血流速度（ＰＦＶＡｃｍ／ｓ）,Ｅ峰面积（Ｅａｒｅａｍ）,舒张早期峰值血流速度与舒张晚期峰值血流速度比（ＰＦＶＥ／ＰＦＶＡ）也高于对照组（Ｐ＜０．０５）。而出现三尖辩肺动脉返流的比例也明显高于对照组（Ｐ＜０．０１）。认为：中长跑运动员不仅心脏形态大小及收缩功能有显著改变,而且在舒张功能也有明显变化     

DISTANCE METHODS: A REPLY TO FARRIS

Abstract— Farris (1985) claimed that my assertions about unbiasedness and consistency of estimates of a phylogeny obtained by least squares fitting are in error. The counterexample he constructed violates the assumptions of additivity and independence of distances which were clearly stated in my earlier paper. As such it is not a valid counterexample. It is argued, contrary to Farris's claims, that one need not avoid nonmetric distances, and that one should avoid negative branch lengths in estimates of phylogenies from distance data. Statistical tests of clockness, and, to a limited extent, of alternative phylogenies can be constructed, and these are demonstrated by example. A computer program to infer phylogenies from distance matrices has been in free distribution by me for several years; it seems as effective as the program recently announced by Farris. Information on phylogenies is present in distance data, as in other kinds of data, and statistical methods can be developed to extract it.     

SPERM WHALE PHYLOGENY REVISITED: ANALYSIS OF THE MORPHOLOGICAL EVIDENCE

Some recent analyses of three mitochondrial DNA regions suggest that sperm whales are the sister group to baleen whales and, therefore, the suborder Odontoceti (toothed whales) constitutes a paraphyletic group. I cladistically analyzed the available morphological data, including that from relevant fossil taxa, for all families of extant cetaceans to test this hypothesis. The results of this analysis unambiguously support a monophyletic Odontoceti including the sperm whales. All synapomorphies that support the Odontoceti node are decisive, not related to the evolution of highly correlated characters, and provide the same result regardless of what order of mammals is used as an outgroup. These numerous, anatomically diverse, and unambiguous characters make this clade one of the best-supported higher-level groupings among mammals. In addition, the fossil evidence refutes a sperm whale/baleen whale clade. Both the molecular and morphological data produce the same unrooted tree. The improper rooting of the molecular tree appears to be producing these seemingly incongruent phylogenies.     

ISOLATION BY DISTANCE IN EQUILIBRIUM AND NON-EQUILIBRIUM POPULATIONS

It is shown that for allele frequency data a useful measure of the extent of gene flow between a pair of populations is , which is the estimated level of gene flow in an island model at equilibrium. For DNA sequence data, the same formula can be used if F_ST is replaced by N_ST. In a population with restricted dispersal, analytic theory shows that there is a simple relationship between M? and geographic distance in both equilibrium and non-equilibrium populations and that this relationship is approximately independent of mutation rate when the mutation rate is small. Simulation results show that with reasonable sample sizes, isolation by distance can indeed be detected and that, at least in some cases, non-equilibrium patterns can be distinguished. This approach to analyzing isolation by distance is used for two allozyme data sets, one from gulls and one from pocket gophers.