vardiff: Function to estimate the variance of the difference between... In SightabilityModel: Wildlife Sightability Modeling

Description

Function to estimate the variance of the difference between two population estimates formed using the same sightability model (to correct for detection).

Usage

 `1` ```vardiff(sight1, sight2) ```

Arguments

 `sight1` Sightability model object for the first population estimate (formed by calling Sight.Est function) `sight2` Sightability model object for the second population estimate (formed by calling Sight.Est function)

Details

Population estimates constructed using the same sightability model will NOT be independent (they will typically exhibt positive covariance). This function estimates the covariance due to using the same sightability model and subtracts it from the summed variance.

Value

 `vardiff` numeric = var(tau^[1])+var(tau^[2])-2*Cov(tau^[1],tau^[2])

John Fieberg

Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19``` ```# Example using moose survey data data(obs.m) # observational moose survey data data(exp.m) # experimental moose survey data data(sampinfo.m) # information on sampling rates # Estimate population size in 2006 and 2007 sampinfo <- sampinfo.m[sampinfo.m\$year == 2007, ] tau.2007 <- Sight.Est(observed ~ voc, odat = obs.m[obs.m\$year == 2007, ], sdat = exp.m, sampinfo.m[sampinfo.m\$year == 2007, ], method = "Wong", logCI = TRUE, alpha = 0.05, Vm.boot = FALSE) tau.2006 <- Sight.Est(observed ~ voc, odat = obs.m[obs.m\$year == 2006, ], sdat = exp.m, sampinfo.m[sampinfo.m\$year == 2006, ], method = "Wong", logCI = TRUE, alpha = 0.05, Vm.boot = FALSE) # naive variance tau.2007\$est[2]+tau.2006\$est[2] # variance after subtracting positvie covariance vardiff(tau.2007, tau.2006) ```

SightabilityModel documentation built on May 29, 2017, 9:37 p.m.