Only the essential minimum information is logged when the skeletal remains arrive, to avoid knowledge of possibly incorrect assumptions made by others. The examination often begins with gender, which is easy to determine if the remains include pelvic bones. Absence of the pubis reduces the accuracy of the determination; the reliability of using skulls is approximately 90 percent. Determining sex in children can be more difficult; teeth are one of the best indicators. Bone measurements and regression equations assist in the determination of height. In addition, different racial groups have different body proportions, but groups overlap in characteristics and determining race can be difficult. The American Academy of Forensic Science maintains a database at the University of Tennessee in Knoxville to improve scientific information on skeletal characteristics in all levels of society. The database also offers the potential for developing custom techniques to analyze particularly difficult cases. Estimating age involves examining all the age indicators in the skeleton, comparing the observations with changes recorded for recent populations of known age, and estimating factors that likely to differ between the remains and the database. An example of the relationship among sex, stature, race, and age is a 1989 murder case from Madison, Wisc. Some cases from Tennessee demonstrate some other factors that may need to be considered in estimating basic parameters from bones. The forensic examination of Penpi, an Egyptian who lived 2,700 years ago, also demonstrates the use of forensic anthropological examination of remains of people from the past.