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Calibrating Population Indices by Double Sampling

L. L. Eberhardt and M. A. Simmons
The Journal of Wildlife Management
Vol. 51, No. 3 (Jul., 1987), pp. 665-675
Published by: Wiley on behalf of the Wildlife Society
DOI: 10.2307/3801286
Stable URL: http://www.jstor.org/stable/3801286
Page Count: 11
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Calibrating Population Indices by Double Sampling
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Abstract

Indices, or relative measures of abundance, provide the practical basis for most management actions but have not been studied quantitatively. A survey sampling technique, known as "double sampling," offers a way to calibrate indices against direct estimates of absolute numbers in a population. This technique is based on an approach known as "ratio estimation," which depends on knowing the values of an auxiliary variable (here, the index of abundance) over all sampling units on a study area. Applications of both techniques to field data on a number of species suggest that they offer opportunities to substantially strengthen the use of population indices. Since the available theory for double sampling (and, to a lesser extent, ratio estimation) is limited in scope, several simulations were conducted to check the existing equations for estimating means and variances. The results indicate that these equations will perform satisfactorily under the circumstances tested. Similar simulations should be conducted in conjunction with field use of the methods.

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