Likelihood Ratio Tests for a Mixture of Two von Mises Distributions

• Published in: Biometrics Vol. 57; no. 1; pp. 260 - 265
• Main Authors: Grimshaw, Scott D., Whiting, David G., Morris, Thomas H.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.03.2001; International Biometric Society
• Subjects: Animals; Bedforms; Biometry; Bones; Circular data; Computer Simulation; Density; Dinosaur bones; Dinosaur fossils; Dinosaurs; Directional data; dunes; Fossils; Geological Phenomena; Geology; Hypothesis testing; Likelihood Functions; Likelihood ratio statistic; Maximum likelihood estimators; Mesas; Mixture; Models, Statistical; Paleoflow direction; Paleontology - statistics & numerical data; Probabilities; Ratio test; Reptiles; rivers; sandstone; Statistics; von Mises distribution
• ISSN: 0006-341X; 1541-0420
• DOI: 10.1111/j.0006-341X.2001.00260.x

It is proposed that the orientation of elongate objects, such as bones, may be used to identify the flow direction of ancient river deposits. If true, elongate objects could be of great value when ancient bedforms such as ripples and dunes are not visible. Two sandstone quarries were investigated wherein the paleoflow direction was determined from both bedforms and elongate dinosaur bones. A mixture of two von Mises distributions captures the observation that elongate bones transported under unidirectional flow conditions will align both parallel and perpendicular to the flow direction. Likelihood ratio tests for a mixture of two von Mises distributions are given. The power of these tests is investigated by simulation since the direction of dinosaur bones agrees with the primary bedforms if the hypothesis test comparing the dominant mean direction of the bones to the paleoflow direction fails to reject. The likelihood ratio test on the dominant mean direction has reasonable power. If the two mean directions in the mixture distribution are π apart, a more powerful likelihood ratio test can be used. The likelihood ratio test on the hypothesis that the two mean directions are exactly π apart is useful in determining if the assumptions of the more powerful test are satisfied.