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

### Description

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

### Usage

1 |

### Arguments

`total` |
Number of animals in each independently sighted group |

`srates` |
Vector of plot-level sampling probabilities (same dimension as |

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

### Value

`tau.hat` |
Sightability estimate of population size, tau^ |

`Vartot` |
Estimated variance of tau^ |

`VarSamp` |
Estimated variance component due to sampling aerial units |

`VarSight` |
Estimated variance component due to sighting process (i.e., series of binomial rv for each animal group) |

`Varmod` |
Estimated variance component due to estimating detection probabilities using test trial data |

### Author(s)

John Fieberg

### 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.

### See Also

`Sight.Est`

, `SS.est`