The Still Bay points of Apollo 11 Rock Shelter, Namibia : an inter-regional perspective

Abstract: Dating to roughly 80,000 to 70,000 years ago, components of the Still Bay technocomplex of southern Africa and their potential behavioural implications have been widely discussed. Stone points with invasive retouch, as defined over 90 years ago by Goodwin and van Riet Lowe, serve as markers for Still Bay assemblages, yet many Still Bay sites remain undated and comprehensive, comparable sets of data for their point assemblages remain unpublished. Much of the Middle Stone Age at the site of Apollo 11 in Namibia was undated until 2010, when a potential Still Bay component was announced. Although a Still Bay assemblage at Apollo 11 would represent the most northwesterly and inland expression of this technocomplex, its points have never been fully analysed. This paper presents their morphometric data and an interpretation of point-production strategies. These results are then compared with data obtained for two South African sites: Hollow Rock Shelter in the Western Cape and Umhlatuzana in KwaZulu-Natal. This comparison demonstrates that whereas there are no statistically significant differences in the morphometric data sets between the three sites, there are both similarities and differences in point-production strategies, cross-section shapes and the use of raw materials for knapping. It is suggested that these similarities and variations represent aspects of how knowledge-transfer systems and knapping conventions were followed on both intra-regional and inter-regional scales

Methods to assess performance of models estimating risk of death in intensive care patients: a review

Models that estimate the probability of death of intensive care unit patients can be used to stratify patients according to the severity of their condition and to control for casemix and severity of illness. These models have been used for risk adjustment in quality monitoring, administration, management and research and as an aid to clinical decision making. Models such as the Mortality Prediction Model family, SAPS II, APACHE II, APACHE III and the organ system failure models provide estimates of the probability of in-hospital death of ICU patients. This review examines methods to assess the performance of these models. The key attributes of a model are discrimination (the accuracy of the ranking in order of probability of death) and calibration (the extent to which the model's prediction of probability of death reflects the true risk of death). These attributes should be assessed in existing models that predict the probability of patient mortality, and in any subsequent model that is developed for the purposes of estimating these probabilities. The literature contains a range of approaches for assessment which are reviewed and a survey of the methodologies used in studies of intensive care mortality models is presented. The systematic approach used by Standards for Reporting Diagnostic Accuracy provides a framework to incorporate these theoretical considerations of model assessment and recommendations are made for evaluation and presentation of the performance of models that estimate the probability of death of intensive care patients. (author abstract