How do round identifiers change over time?
In Round 5 we had AIDs composed with household numbers from 1 to n within a population point. Starting with Round 6, BID, CID, DID, and next-rounds *IDs have household numbers from 1 to n within a census district. So, for many Round 6 households BID and AID will not match, although the household is the same. And we made another global change in numeration in Round 15: two-digit household numbers in *IDs were replaced with three-digit household numbers. Each data file has IDs for all previous rounds. A very good tip is NEVER calculate a previous round ID based on next-round ID. It is a really wrong way, it is strictly prohibited! (Although it can give good results for many cases within Rounds 6 till 14, it also gives wrong results too!) We supply all previous *IDs each round to make sure that the linking is made correctly.
