Variance Stabilization Revisited: A Case For Analysis Based On Data Pooling
AuthorFowler, A. M.
AffiliationSchool of Geography, Geology and Environmental Science, The University of Auckland
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Collection InformationThis item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at firstname.lastname@example.org.
CitationFowler, A.M., 2009. Variance stabilization revisited: A case for analysis based on data pooling. Tree-Ring Research 65(2):129-146.
AbstractThe traditional approach to standardizing tree-ring time series is to divide raw ring widths by a fitted curve. Although the derived ratios are conceptually elegant and have a more homogenous variance through time than simple differences, residual heteroscedasticity associated with variance dependence on local mean ring width may remain. Incorrect inferences about climate forcing may result if this heteroscedasticity is not corrected for, or at least recognized (with appropriate caveats). A new variance stabilization method is proposed that specifically targets this source of heteroscedasticity. It is based on stabilizing the magnitude of differences from standardization curves to a common reference local mean ring width and uses data pooled from multiple radii. Application of the method to a multi-site kauri (Agathis australis (D. Don) Lindley) data set shows that (a) the heteroscedasticity issue addressed may be generic rather than radius-specific, at least for some species, (b) variance stabilization using pooled data works well for standardization curves of variable flexibility, (c) in the case of kauri, simple ratios do not appear to be significantly affected by this cause of heteroscedasticity, and (d) centennial-scale variance trends are highly sensitive to the analytical methods used to build tree-ring chronologies.