Biomedical subjects

Samantha R Cook

Publications and source records attributed to Samantha R Cook.

3 recordsLinked to original sources

PubMed2005

Analysis of ochres from Clearwell Caves: the role of particle size in determining colour.

Three ochre samples (A (orange-red in colour), B (red) and C (purple)) from Clearwell Caves, (Gloucestershire, UK) have been examined using an integrated analytical methodology based on the techniques of IR and diffuse reflectance UV-visible-NIR spectroscopy, X-ray diffraction, elemental analysis by ICP-AES and particle size analysis. It is shown that the chromophore in each case is haematite. The differences in colour may be accounted for by (i) different mineralogical and chemical composition in the case of the orange ochre, where higher levels of dolomite and copper are seen and (ii) an unusual particle size distribution in the case of the purple ochre. When the purple ochre was ground to give the same particle size distribution as the red ochre then the colours of the two samples became indistinguishable. An analysis has now been completed of a range of ochre samples with colours from yellow to purple from the important site of Clearwell Caves.

Calcium Carbonate↗

PubMed2004

Antisaccade performance in biological relatives of schizophrenia patients: a meta-analysis.

Poor performance on the antisaccade (AS) task has been interpreted as a potential indicator of genetic liability that may enhance the power of linkage studies of a multidimensional phenotype for schizophrenia. Every study has replicated the finding of significantly worse performance in schizophrenia patients regardless of which specific antisaccade paradigm was employed. In some studies involving a standard version of the antisaccade task, relatives of schizophrenia patients made an increased number of errors, but in other studies that used this same paradigm, relatives of schizophrenia patients did not differ from controls. In this paper, we report the results of a meta-analysis on studies that used the standard antisaccade paradigm. The meta-analysis shows that those studies that reported large effect sizes and statistically significant differences between relatives of schizophrenia patients and controls used inclusion/exclusion criteria that were not symmetrical between the two groups, whereas those studies that reported small and nonsignificant differences between relatives of schizophrenia patients and controls used symmetrical inclusion/exclusion criteria. Specifically, studies that applied stricter psychopathology exclusion criteria to controls than to relatives of schizophrenia patients had larger effect sizes than studies that applied comparable exclusion criteria to both groups, suggesting that antisaccade performance is compromised by psychopathology in general rather than by schizophrenia per se. Since symmetrical inclusion/exclusion criteria between relatives of schizophrenia patients and controls are essential for a genetic analysis, and those studies that did apply symmetrical criteria had small effect sizes, the available data suggest that poor antisaccade performance is unlikely to be useful in identifying clinically unaffected carriers of genes for schizophrenia.

Genotype↗

PubMed2004

A note on testing for homogeneity among effect sizes sharing a common control group.

L. V. Hedges and I. Olkin (1985) presented a statistic to test for homogeneity among correlated effect sizes and L. J. Gleser and I. Olkin (1994) presented a large-sample approximation to the covariance matrix of the correlated effect sizes. This article presents a more exact expression for this covariance matrix, assuming normally distributed data but not large samples, for the situation where effect sizes are correlated because a single control group was compared with more than one treatment group. After the correlation between effect sizes has been estimated, the standard Q statistic for correlated effect sizes can be used to test for homogeneity. This method is illustrated using results from schizophrenia research.

Humans↗