Cluster Sample Size

Example

This program is set up to determine the standard error of the density given three choices for n (e.g. the number of transects: n1, n2, n3), a range of the number of bins per transect and the assumed cluster variance. See the section on cluster sampling for more details on this method.

The cluster variance (s²_clu) and the standard error of the estimated average number per bin (SE()) may be found as:

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where:
P_i is the agregate density in cluster i;
 is the average number per bin over all clusters;
m_i is the number of elements (bins) in cluster i, i = 1,…, n;
n is the number of clusters in the simple random sample of clusters (transects); and
is the estimated average number of elements (bins) per cluster (transect), such that

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The cluster variance, which is the variation in the agregate density, may be calculated from data collected in a previous or pilot survey. You may wish to use the value provided from the Cluster Sampling Analysis routine applied to your data. The value of 0.57, provided as a default in this example run, comes from a survey of smelt in Lake Champlain.