# Wong.est.Ratio: Sightability estimate of ratio with variance components... In SightabilityModel: Wildlife Sightability Modeling

 Wong.est.Ratio R Documentation

## Sightability estimate of ratio with variance components estimator from Wong (1996)

### Description

Estimates population ratio, with variance estimated using Wong's (1996) estimator. This function will usually be called by Sight.Est,Ratio() function (but see details).

Wong.est.Ratio(
numerator,
denominator,
srates,
nh,
Nh,
stratum,
subunit,
covars,
beta,
varbeta,
smat = NULL
)

### Arguments

 numerator, denominator Number of animals in numerator and denominator of each independently sighted group srates Vector of plot-level sampling probabilities (same dimension as total). nh Number of sample plots in each stratum Nh Number of population plots in each stratum stratum Stratum identifiers (associated with the independently observed animal groups) subunit Plot ID (associated with the independently observed animal groups) covars Matrix of sightability covariates (associated with the independently observed animal groups) beta Logistic regression parameter estimates (from fitted sightability model) varbeta Estimated variance-covariance matrix for the logistic regression parameter estimates (from fitted sightability model) smat Estimated variance-covariance matrix for the inflation factors (1/probability of detection). This is an n.animal x n.animal matrix, and is usually calculated within the Wong.est function. Non-null values can be passed to the function (e.g., if a bootstrap is used to estimate uncertainty due to the estimated detection parameters).

### Details

This function is called by Sight.Est.Ratio, but may also be called directly by the user (e.g., in cases where the original sightability [test trial] data are not available, but the parameters and var/cov matrix from the logistic regression model is available in the literature).

### Value

 ratio.hat Sightability estimate of ratio, ratio^ Vartot Estimated variance of ratio^ VarSamp, VarSight, VarMod Estimated variance component due to sampling, sightability, model are set to NA

### Author(s)

Carl James Schwarz cschwarz.stat.sfu.ca@gmail.com

### References

Rice CG, Jenkins KJ, Chang WY (2009). Sightability Model for Mountain Goats." The Journal of Wildlife Management, 73(3), 468- 478.

Steinhorst, R. K., and M.D. Samuel. (1989). Sightability adjustment methods for aerial surveys of wildlife populations. Biometrics 45:415-425.

Wong, C. (1996). Population size estimation using the modified Horvitz-Thompson estimator with estimated sighting probabilities. Dissertation, Colorado State University, Fort Collins, USA.