Dear Nick To understand the effects of the 'nugget' effect on parameter estimates I recommend you have a read of the various sections Noel Cressie's 'Spatial Statistics'. Kind Regards Vince Vince Matassa Department Of Agriculture BIOMETRICS SECTION University Of Queensland Brisbane 4072 Australia -- Asreml mailinglist archive: http://www.chiswick.anprod.csiro.au/lists/asreml