For two realistic (but not real) populations of loblolly pine, variance estimators for weighed regression estimates of total volume are compared. The traditional variance estimators and two robust variance estimators proposed by Royall and Cumberland (R. M. Royall and W. G. Cumberland. 1981. JASA, J. Am. Stat. Assoc. 76: 924–930) are found to be quite unreliable. In contrast, the jackknife variance estimate and confidence intervals based on it are found to be much more reliable.
The sampling distribution of the index of' dispersion is investigated under each of t8hree distributions for the quadrat counts, namely the Poisson, negative binomial and binomial distributions. Approximations to the sampling distributions are constructed and are evaluated using a computer simulation study.
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