- For the measure of downside risk, see Variance#Semivariance
In spatial statistics, the empirical semivariance is described by semivariance=1/2(z(x)-z(x))^2 where z is the attribute value
where z is a datum at a particular location, h is the distance between ordered data, and n(h) is the number of paired data at a distance of h. The semivariance is half the variance of the increments , but the whole variance of z-values at given separation distance h (Bachmaier and Backes, 2008).
A plot of semivariances versus distances between ordered data in a graph is known as a semivariogram rather than a variogram. Many authors call a variogram, others use the terms variogram and semivariogram synonymously. However, Bachmaier and Backes (2008), who discussed this confusion, have shown that should be called a variogram, terms like semivariogram or semivariance should be avoided.
- Bachmaier, M and Backes, M, 2008, "Variogram or semivariogram? Understanding the variances in a variogram". Article doi:10.1007/s11119-008-9056-2, Precision Agriculture, Springer-Verlag, Berlin, Heidelberg, New York.
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- Shine, J.A., Wakefield, G.I.: A comparison of supervised imagery classification using analyst-chosen and geostatistically-chosen training sets, 1999, https://web.archive.org/web/20020424165227/http://www.geovista.psu.edu/sites/geocomp99/Gc99/044/gc_044.htm
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