When is it meaningful to estimate an extinction probability?

Recently Don Ludwig has shown that calculations of extinction probabilities based on currently available data are often meaningless due to the large u ncertainty accompanying the estimates. Here we address two questions posed by his findings. Can one ever calculate extinction probabilities accurately ? If so, how much data would be necessary? Our analysis indicates that reli able predictions of long-term extinction probabilities are likely to requir e unattainable amounts of data. Analytic calculations based on diffusion ap proximations indicate that reliable predictions of extinction probabilities can be made only for short-term time horizons (10% to 20% as long as the p eriod over which the population has been monitored). Simulation results for unstructured and structured populations (three stage classes) agree with t hese calculations.