The recent market decline has many analysts and traders alike calling for a bear market. Birinyi Associates analyzed the current market correction (it will not be a defined bear market unless the S&P closes at or below 1252.12) and using the intra-day price of 1277.15 the market was 18.4% below its high close.
Looking at all 10%+ corrections since 1962, the average decline was -18% and lasted 136 days. The average decline since the 1982 rally is 17% (16% ex '87).(Note that some corrections did result in a bear market.)