CRAIG ESTIMATOR 2.0
free program for population size estimation from mark-recapture data
WHAT IS CRAIG ESTIMATOR?
Craig Estimator is a freely available utility for population size estimation using mark-recapture data. It is based on the Craig's model (see Craig C.C. 1953: On the utilization of marked specimens in estimating populations of flying insects. Biometrika 40: 170-176).
CRAIG ’S MODEL IN MORE DETAIL
Capture-recapture experiments (also mark recapture
or capture release recapture experiments) are
experiments where an observer catches animals,
marks them, and immediately releases them. Then
he catches animals from the same population again,
records marked individuals, and marks unmarked
individuals. In his paper, C.C. Craig 1953 has
formulated six methods for estimating population
size of insects from capture-recapture data. Craig
Estimator uses the first of the methods, Method 1.
The model According to the Craig’s model, population size n can be estimated from:
log n - log (n - r) = s / n
where r is the number of captured individuals, and s is the overall number of captures (how many times these individuals were captured altogether). Craig
Estimator uses the bisection method to solve the equation. Standard deviation of the estimate,
95% confidence interval, and lower and upper confidence limits are then calculated.
Assumptions
Craig’s model has assumptions about the design of mark recapture experiments These are:
- individuals are marked and released back to the population
- catchability is same for all individuals (marked and unmarked)
- the study population is stable during the sampling period
- the model is designed for closed populations (individuals may not immigrate to or emigrate from the study population). However, it can also be used for open populations if the sampling period is short and thus effects of immigration and emigration of are negligible.
HOW TO GET CRAIG ESTIMATOR?
The link to download Craig Estimator 2.0 is available below. You
must have Java Runtime Environment installed on your computer to run the program.
For more information write an e-mail to: pav.sebek[at]gmail.com.
