title: Integrated survival analysis using an event-time approach in a Bayesian framework.
abstract: Event-time or continuous-time statistical approaches have been applied throughout the biostatistical literature and have led to numerous scientific advances. However, these techniques have traditionally relied on knowing failure times. This has limited application of these analyses, particularly, within the ecological field where fates of marked animals may be unknown. To address these limitations, we developed an integrated approach within a Bayesian framework to estimate hazard rates in the face of unknown fates. We combine failure/survival times from individuals whose fates are known and times of which are interval-censored with information from those whose fates are unknown, and model the process of detecting animals with unknown fates. This provides the foundation for our integrated model and permits necessary parameter estimation. We provide the Bayesian model, its derivation, and use simulation techniques to investigate the properties and performance of our approach under several scenarios. Lastly, we apply our estimation technique using a piece-wise constant hazard function to investigate the effects of year, age, chick size and sex, sex of the tending adult, and nesting habitat on mortality hazard rates of the endangered mountain plover (Charadrius montanus) chicks. Traditional models were inappropriate for this analysis because fates of some individual chicks were unknown due to failed radio transmitters. Simulations revealed biases of posterior mean estimates were minimal (≤ 4.95%), and posterior distributions behaved as expected with RMSE of the estimates decreasing as sample sizes, detection probability, and survival increased. We determined mortality hazard rates for plover chicks were highest at <5 days old and were lower for chicks with larger birth weights and/or whose nest was within agricultural habitats. Based on its performance, our approach greatly expands the range of problems for which event-time analyses can be used by eliminating the need for having completely known fate data.
authors.affiliation: National Wildlife Health Center, United States Geological Survey 6006 Schroeder Road, Madison, Wisconsin, 53711.
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Walsh
authors.affiliation: Wildlife Biology Program and Avian Science Center, College of Forestry and Conservation, University of Montana Montana, 59812.
authors.forename: Victoria J
authors.initials: VJ
authors.lastname: Dreitz
authors.affiliation: National Wildlife Health Center, United States Geological Survey 6006 Schroeder Road, Madison, Wisconsin, 53711.
authors.forename: Dennis M
authors.initials: DM
authors.lastname: Heisey
keywords: Charadrius montanus; continuous time; detection probability; event time; hazard rate; mountain plover; simulation; survival; unknown fate