Despite the slender evidentiary base of surviving sources, historians would dearly like to know more about colonial vital rates. In the absence of hard data, speculation has run rampant about changes in fertility and mortality. Were African birth rates always as high as they are today? Did the early years of colonial rule bring about rises in the deathrates in all areas and to the same degree? Researchers are now combing the available evidence for materials to answer questions such as these.

Unfortunately, the records of a single year's births and deaths are not a reliable indicator of long-term demographic trends. In a small population in particular, the events of a given year must be seen in the context of the years surrounding it. Inadequate reporting might lead to underestimates of either fertility or mortality rates, while uncommon events such as epidemics might be wrongly taken as typical.

These discontinuities have led researchers to concentrate on series of demographic rates rather than isolated estimates. Mathematically, this has promoted the use of techniques which convert the haphazard incidences of births and deaths into continuous functions which, although not as close to the raw data as year-by-year statistics, nonetheless give the reader a notion of trends over time.