------------------------------------------------------ URA 2055 ----------------
 Author(s) :
             THIOULOUSE J.,ROYET J.P.,PLOYE H.,HOULLIER F.
             Evaluation of the Precision of Systematic Sampling : Nugget Effect
             and Covariogram Modelling
             Journal of Microscopy
             Serial Number : 172, 1993, pp. 249-256
             ISSN : 0022-2720

 Key-Words :
             STEREOLOGY,VOLUME ESTIMATION,SERIAL SECTIONS,SYSTEMATIC SAMPLING,
             SAMPLING INTENSITY,SAMPLING PRECISION,REGIONALIZED VARIABLES,
             NUGGET EFFECT,OLFACTORY BULB,RODENT,TRANSITIVE COVARIOGRAM,
             MORPHOMETRIC ESTIMATIONS


 Abstract      Systematic sampling designs are widely used in stereology. When
             an estimator of the total amount, Q, of the sampled variable is
             evaluated by such a procedure, the coefficient of error can be
             predicted by applying Matheron's theory of regionalized variables.
             To evaluate the accuracy of the estimate of Q, it is necessary to
             study the behaviour of the regionalized variable and to model its
             covariogram. Histological data with a low short-range variability
             and agronomic data with a pronounced nugget effect provided the
             biological material for extreme case studies. Results show that
             the short-range variability, if present, cannot be detected when
             only small samples are available. An underestimation of the
             coefficient of error is then to be expected. We propose several
             models of the covariogram, which can be used to test for presence
             of a nugget effect. If a nugget effect is present, these models
             will provide better estimates of the coefficient of error. If
             there is no nugget effect the simplified method of Gundersen and
             Jensen (1987) can be used and will provide reliable estimates of
             the coefficient of error.

 E-Mail :    thioulou@biomserv.univ-lyon1.fr
             Laboratoire de Biometrie, Genetique et Biologie des Populations
             (URA 2055) - Univ. C. Bernard LYON I - 69622 VILLEURBANNE CEDEX