Showing papers by "Anne Chao published in 2000"

Estimating the number of shared species in two communities

Abstract: In statistical ecology, the number of shared species is a standard measure of similarity between two communities. Assume that a multinomial sample is drawn from each of the two target communities. Each observation (individual) in the sample is classified to species identity, and the frequency for each observed species is recorded. This paper uses the concept of sample coverage to estimate the number of species in common to the two communities (the number of shared species). The result generalizes Chao and Lee (1992) to a two-community situation. Simulation results are reported to examine the performance of the proposed estimators. Bird census data collected from April 1994 to March 1995 in Ke-Yar and Chung-Kang estuaries in Taiwan are used to illustrate the estimation procedure.

Seasonal variation in suicides: diminished or vanished. Experience from England and Wales, 1982-1996.

Abstract: Background Seasonal variation in suicidal death has been observed in many countries. In particular, a cyclic variation was found for both men and women in England and Wales in the 1960s and 1970s. Men showed a single 12-month cycle whereas women showed two cycles. Aims To re-examine the seasonal variation in suicides in England and Wales for the period 1982-1996. Method A harmonic analysis was used to detect the seasonality of the suicide data. Results The seasonal effect on suicide is greatly diminished in England and Wales. This is shown by the reduced amplitude and smaller proportion of variance accounted for by the season. Conclusions The seasonal effect on suicide has either diminished or vanished.

Capture-recapture when time and behavioral response affect capture probabilities.

Abstract: We consider a capture-recapture model in which capture probabilities vary with time and with behavioral response. Two inference procedures are developed under the assumption that recapture probabilities bear a constant relationship to initial capture probabilities. These two procedures are the maximum likelihood method (both unconditional and conditional types are discussed) and an approach based on optimal estimating functions. The population size estimators derived from the two procedures are shown to be asymptotically equivalent when population size is large enough. The performance and relative merits of various population size estimators for finite cases are discussed. The bootstrap method is suggested for constructing a variance estimator and confidence interval. An example of the deer mouse analyzed in Otis et al. (1978, Wildlife Monographs 62, 93) is given for illustration.

Estimating the population size with a behavioral response in capture-recapture experiment

Abstract: A new estimating procedure is suggested to estimate the population size in a capture-recapture experiment. The capture intensities for first-capture and recapture are allowed to be different and time dependent but they are assumed to be proportional. It is shown that the information on the proportionality constant is crucial to the estimation of the population size. Sensitivity analysis with a misspecification of the proportionality constant is conducted. The method has also been extended to the case with an unknown proportionality. A real example is given.