fishmethods (version 1.12-1)

deltadist: 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)

Value

vector containing the delta mean and associated variance.

Arguments

x

vector of catch values, one record for each haul. Include zero and nonzero catches. Missing values are deleted prior to estimation.

Author

Gary A. Nelson, Massachusetts Division of Marine Fisheries

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).

References

Pennington, M. 1983. Efficient estimators of abundance for fish and plankton surveys. Biometrics 39: 281-286.

Examples

data(catch)
deltadist(catch$value)