Compositional data analysis of archaeological glass: problems and possible solutions

Presentation in CODAWORK'03, session 4: Applications to archeometry

Compositional analysis of archaeological glasses

At CoDaWork'03 we presented work on the analysis of archaeological glass composi- tional data. Such data typically consist of geochemical compositions involving 10-12 variables and approximates completely compositional data if the main component, sil- ica, is included. We suggested that what has been termed `crude' principal component analysis (PCA) of standardized data often identi ed interpretable pattern in the data more readily than analyses based on log-ratio transformed data (LRA). The funda- mental problem is that, in LRA, minor oxides with high relative variation, that may not be structure carrying, can dominate an analysis and obscure pattern associated with variables present at higher absolute levels. We investigate this further using sub- compositional data relating to archaeological glasses found on Israeli sites. A simple model for glass-making is that it is based on a `recipe' consisting of two `ingredients', sand and a source of soda. Our analysis focuses on the sub-composition of components associated with the sand source. A `crude' PCA of standardized data shows two clear compositional groups that can be interpreted in terms of di erent recipes being used at di erent periods, re ected in absolute di erences in the composition. LRA analysis can be undertaken either by normalizing the data or de ning a `residual'. In either case, after some `tuning', these groups are recovered. The results from the normalized LRA are di erently interpreted as showing that the source of sand used to make the glass di ered. These results are complementary. One relates to the recipe used. The other relates to the composition (and presumed sources) of one of the ingredients. It seems to be axiomatic in some expositions of LRA that statistical analysis of compositional data should focus on relative variation via the use of ratios. Our analysis suggests that absolute di erences can also be informative

[Ressenya del llibre Rediscovering geography: new relevance for science and society, de Rediscovering Geography Committee, National Research Council]

El llibre ressenyat pretén ser una síntesi i una avaluació de la situació de la geografia als Estats Units. Estructurat en vuit capítols, els sis primers són una anàlisi de diversos aspectes de la geografia i els dos últims expliquen quina estratègia hauria de portar-se a terme per enfortir el paper de la geografia en el món acadèmic i en la societat en general

Didactics–promoting collaborative work and personal learning environment. Critical, creative and autonomous roles in a competitive society

School has evolved from a place where knowledge is provided to a place where learners are helped to develop their professional and social skills. Consequently, education must evolve through big challenges in order to face the changes of society in the XXIst century

SILEX: la Infraestructura de Datos Espaciales del yacimiento arqueológico de Casa Montero

El objetivo es presentar la experiencia de utilización del Software Libre y de Código Abierto en el desarrollo e implantación del Sistema de Información (SI) del yacimiento arqueológico de Casa Montero. Se muestra el potencial de combinar las Infraestructuras de Datos Espaciales y las bases de datos orientadas a grafos en la gestión, investigación y difusión del Patrimonio Arqueológico (PA). Se ejemplifica la propuesta tecnológica a través del ejemplo de SI del yacimiento arqueológico de Casa Montero (Madrid), SILEX (Sistema de Información Locacional en XML). La implementación de sistemas de información para la gestión de PA colabora fuertemente en tres actividades básicas que han de ser realizadas sobre él. En primer lugar, la gestión, con el objetivo de protegerlo y conservarlo; en segundo término, la investigación, de cara a elaborar conocimiento histórico mediante el análisis arqueológico de los restos materiales del pasado; y en tercer lugar, la difusión, con la pretensión de divulgar el PA y el conocimiento histórico generado a partir del mismo entre la sociedad