[DDI-users] Documenting rates in the aggregate data extension

[Humphrey Southall]

The DDI aggregate data extension is very clearly designed to document 
tables consisting mainly of frequency counts.  What should we do with 
pre-computed percentages?

My project is converting existing machine-readable transcriptions of tables 
from British census reports to a structure which uses DDI-based metadata, 
and most of the columns in those tables are just such counts of numbers of 
people.

They also contain columns which are pre-computed rates, generally 
percentages.  Most of them can be derived directly from counts held in 
other columns in the same table, and so far we have mostly ignored 
them;  we are not discarding them, as the system will also hold spreadsheet 
versions of the original tables, but they will not be easily located, or 
accessible to our visualisation tools.

However, there are some rates in the reports which contain information not 
available in any other form.  The most immediate issue is with data in the 
main parish-level table from the 1951 census for England and Wales.  This 
includes population density, which can easily be computed from figures for 
population and area, and "Persons per Room", computable from the number of 
persons and the numbers of rooms in private households.  However, it also 
includes "Percentage of persons at more than 2 per Room".  Although another 
table gives plenty of information about numbers of people versus numbers of 
room, by household, for c. 1,500 districts from which this rate could be 
computed, no other information is available for the c. 15,000 
parishes.  The micro-data are official secrets until 2052, and as far as we 
can establish no unpublished intermediate calculations from pre-1971 
censuses survive anywhere -- so this is really interesting data.

How can we include these data values in our system?  I can see that just 
about any number can be held in a non-additive nCube, but that greatly 
limits what we can do with it.  Is there another structure we should be using?

Best wishes,

Humphrey Southall
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Humphrey Southall
Reader in Geography/Director,
Great Britain Historical GIS Project
Department of Geography, University of Portsmouth
Buckingham Building, Lion Terrace, Portsmouth PO1 3HE

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