Note that a fair part of the time data must be adjusted for legitimate
reasons. Yugoslavia splintered into Bosnia and Herzegovina (still
together), Croatia, Slovenia, Serbia and Montenegro, and Macedonia.
Subsequently, Montenegro went its own way, and it appears Kosovo will
follow. In contrast, two Germanies merged. Today, some sort of
mathematical history will have to be created for the new country
emerging from southern Sudan, while figures will have to be adjusted
for the continuing Sudan.
When it comes to sub-countries Libya is particularly notorious for
reorganizing every few years. World-wide, we average changes to nearly
sixty sub-countries per year.
There is an additional problem: countries tend to report economic
measures in gross amounts - imports might be reported in hundreds of
million of US dollars, for example. In order to fairly compare across
countries we normalize by dividing through by population. This means
that the accuracy of many measures can be adversely impacted by
population if there are imprecise demographics. We hasten to add that
population is NEVER correct - people (citizens or not) are constantly
being born, dying or moving. No (zero) countries maintain a continuous
count. Doing a census is comparatively slow both to count and report,
not always accurate, and almost never synchronized even with
neighboring countries. Fortunately, it is usually the case that close
enough is close enough, so a population estimate with random errors
(as opposed to systematic miscounts) within one percent is tolerable.