Journal
BIOMETRICS
Volume 57, Issue 1, Pages 211-218Publisher
WILEY
DOI: 10.1111/j.0006-341X.2001.00211.x
Keywords
bandwidth; binning; covariance function; isotropy; kernel function; nonparametric regression; permutation test; quadratic form; smoothing techniques; spatial data; stationarity; variogram
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The variogram is a standard tool in the analysis of spatial data, and its shape provides useful information on the form of spatial correlation that may be present. However, it is also useful to be able to assess the evidence for the presence of any spatial correlation. A method of doing this, based on an assessment of whether the true function underlying the variogram is constant, is proposed. Nonparametric smoothing of the squared differences of the observed variables, on a suitably transformed scale, is used to estimate variogram shape. A statistic based on a ratio of quadratic forms is proposed and the test is constructed by investigating the distributional properties of this statistic under the assumption of an independent Gaussian process. The power of the test is investigated. Reference bands are proposed as a graphical follow-up. An example is discussed.
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