The rural classes constituted the overwhelming majority of all the Scandinavian populations in the Viking Age. Osteologists and osteo-archaeologists have provided new and invaluable data which can be used by historical demographers to provide information on life expectancy and mortality. Danish and Norwegian osteological studies on sizable Iron Age skeletal materials consistently show mean life expectancy at age twenty of only 15-18 years. The type and size of co-residential units are fundamentally important demographic structures. According to a composite estimate, the mean size of a simple family household occupying a usual Scandinavian holding around 1300 would be about 4.25 persons. This average would be slightly increased, to about 4.5 persons, by a modest element of living-in servants and lodgers and by the infrequent occurrence of joint (biologically related) or multiple (unrelated) families. In the second half of the thirteenth century, Denmark's population was much larger than that of any other Nordic country.