The Statewide Database presents a 1990 census tract to 2000 census tract conversion file.

TO USE:

If you have a dataset arranged by 1990 census tract, this file can be used to approximate
this data by 2000 census tract.  In order to use this file, you need to join your 1990 dataset
to the conversion file using the 1990 tract field.  This field is identical to those used in
the TIGER files throughout the 90s.  Note that you will have duplicate lines in your data.

At this point, multiply the "PERCENT" by each of your data elements in the joined line.

Next, aggregate the resulting products according to the field under 2000 tract, which is
the TIGER identifier for the new tracts.

That's all!


HOW WE MADE THE CONVERSION:

We made this conversion using a very simple allocation of 1990 population depending on the percentage of
people from that geography ending up in each 2000 tract.  Thus each line of the conversion 
file contains the following information:

TRACT2000  The number of the 2000 tract under question
TRACT1990  The number of the 1990 tract under question
2000POP    The 2000 census count of population for this 2000 tract.
1990POP    The 2000 census count of population in this 1990 tract.
overlap    The number of people from this 1990 tract that should reside in the corresponding 2000 tract
PERCENT    The percentage of this 1990 tract that should be allocated to this 2000 tract.

So how did we get the 1990POP figure?  This was done with GIS, 
by tagging the 2000 census blocks with a corresponding 1990 census block number.  The 1990 tracts could
be aggregated from this overlay.