probnzeros: Get probability of zero bycatch given effort

In kacurtis/obscov4CV: Evaluate Fishery Observer Coverage for Bycatch Estimation

Get probability of zero bycatch given effort

Description

probnzeros returns probability of zero bycatch in a specified number of effort units, given bycatch per unit effort and dispersion index.

Usage

probnzeros(n, bpue, d)

Arguments

n	a vector of positive integers. Observed effort levels (in terms of effort units, e.g., trips or sets) for which to calculate probability of zero bycatch.
bpue	a positive number. Bycatch per unit effort.
d	a number greater than or equal to 1. Dispersion index. The dispersion index corresponds to the variance-to-mean ratio of effort-unit-level bycatch, so d = 1 corresponds to Poisson- distributed bycatch, and d > 1 corresponds to overdispersed bycatch.

Details

Calculated from the probability density at zero of the corresponding Poisson (d = 1) or negative binomial (d > 1) distribution.

Caveat: probnzeros assumes that (1) observer coverage is representative, (2) bycatch (bpue) is in terms of individuals (not weight) per unit effort, and (3) the specified dispersion index reflects the highest level of any hierarchical variance (e.g., using dispersion index at trip level if greater than that at set level). Violating these assumptions will likely result in negatively biased projections of the probability of observing zero bycatch at a given level of observer coverage. More conservative projections can be obtained by using a higher dispersion index d. Users may want to explore uncertainty in dispersion index and in bycatch per unit effort by varying those inputs.

Value

Vector of same length as n with probabilities of zero bycatch.

Returned invisibly

kacurtis/obscov4CV documentation built on Feb. 4, 2024, 8:31 p.m.