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

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Description

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

Usage

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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)

NOTE: sight1 should correspond to the tau^[t], and sight2 to tau^[t+1]

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

See Also

vardiff

Examples

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# 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)