# varlog.lam: Calculates the variance of the log rate of change between 2... In SightabilityModel: Wildlife Sightability Modeling

 varlog.lam R Documentation

## Calculates the variance of the log rate of change between 2 population estimates that rely on the same sightability model.

### Description

Calculates the variance of the log rate of change between 2 population estimates that rely on the same sightability model.

### Usage

``````varlog.lam(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

This function uses the delta method to calculate an approximate variance for the log rate of change, log(tau^[t+1])-log(tau^[t]), while accounting for the positive covariance between the two estimates (as a result of using the same sightability model to correct for detection).

### Value

 `loglambda` log rate of change = log(tau^[t+1]/tau^[t]) `varloglamda` approximate variance of loglambda

### Author(s)

John Fieberg

`vardiff`

### Examples

``````
# 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)

# Log rate of change
varlog.lam(tau.2006, tau.2007)

``````

SightabilityModel documentation built on May 2, 2023, 1:12 a.m.