| deltadist {fishmethods} | R Documentation |
Delta Distribution Mean and Variance Estimators
Description
Calculates the mean and variance of a catch series based on the delta distribution described in Pennington (1983).
Usage
deltadist(x = NULL)
Arguments
x |
vector of catch values, one record for each haul. Include zero and nonzero catches. Missing values are deleted prior to estimation. |
Details
Data from marine resources surveys usually contain a large proportion of hauls with no catches. Use of the delta-distribution can lead to more efficient estimators of the mean and variance because zeros are treated separately. The methods used here to calculate the delta distribution mean and variance are given in Pennington (1983).
Value
vector containing the delta mean and associated variance.
Author(s)
Gary A. Nelson, Massachusetts Division of Marine Fisheries gary.nelson@mass.gov
References
Pennington, M. 1983. Efficient estimators of abundance for fish and plankton surveys. Biometrics 39: 281-286.
Examples
data(catch)
deltadist(catch$value)