All three kinds of data typically are recorded at the level of the geologic stage, or epoch in the case of the Carboniferous and sometimes Middle and Late Permian. Devonian to Pleistocene stages are time units that range in duration from 1.3 (Induan) to 18.3 (Visean) m.y., with a mean length of ≈7.1 m.y (Fig. 3)., although these values are subject to significant change as better calibration methods become available. The level of taxonomic analysis can range from the species to the order. Traditionally analysis has been at the level of the family, owing mostly to the practical issue of compiling a vast database of fossil insect taxa at lower ranks (genera and species occurrence data currently are being assembled by several researchers