detect.prop {emon}

Probability of detecting a feature that covers a proportion theta of the survey area.

Description

The function can calculate the probability of a feature that occupies a proportion theta of the sampling area and where the sampling point density of the survey is specified; the sampling point density needed to achieve a specified probability of detection, where theta is also specified ; or the value of theta that will be detected with specified probability and sampling density.Unless the feature is made of a large number of random segments (see below for how to deal with this situation), these methods apply only when the pattern of points in the sampling deisgn is random.

Usage

detect.prop(statistic, theta=NA, pdetect=NA, ssize=NA)

Arguments

statistic

Describes what aspect of design you want calculated. The choices are "P" (probability detection); "N" (sample size) or "F" (feature proportion).

theta

Feature proportion. Not needed if statistic="F".

pdetect

Probability detection. Not needed if statistic="P".

ssize

Sample size. Not needed if statistic="N".

Details

The probability of detection is p = 1 - (1 - theta)^{N}. Formulae for theta and N are readily obtained from this formula. If the spatial pattern of the feature consists of lots of small, random uniformly distributed fragments, then we can redefine theta = Na/A where a is the area of the sampling unit and A is the sampling area.In this situation, the probability of patch detection applies no matter what the spatial pattern of points in the sampling design. Unlike detect, detect.prop works for vectors - so long as the input vectors are of the same length.

Value

prob

Probability of detection

ssize

Sample size

prop

Feature proportion

Author(s)

Jon Barry: [e-mail]

Examples

detect.prop(statistic='P', theta=0.02, ssize=80)
detect.prop(statistic='N', theta=0.02, pdetect=0.9)
detect.prop(statistic='F', pdetect=0.9, ssize=80)