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

## Description

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

## Usage

 `1` ```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`
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16``` ```# 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) ```