varlog.lam: Calculates the variance of the log rate of change between 2...

Description Usage Arguments Details Value Author(s) See Also Examples

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)


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