2011 / 2011 data comparisons

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Introduction
Based upon user feedback about the lack of comparison data in 2001 Census releases, user expectations for the facility to compare data from the 2011 Census with that from 2001 should be considerable.

There are major challenges involved in producing intercensal change figures for small areas or populations becuase of the differences between Censuses. For 2001/2011, these include changes both in geography, and in statistical differences such as changes in questions/definitions/output classifications and methodological concerns such as population base and coverage/imputation. There are also potential disclosure issues related to differencing which may arise due to any re-issue of 2001 statistics.

Resolving these issues requires a robust solution based on development work building from research to identify sources of, and methods to metigate the impact of, some of the intercensal variability.

It is important to remember that exact comparison will not be possible for many 2001 and 2011 figures, and that any measure of change must be qualified by information on the broad statistical significance of the apparent change. Extra consideraion will need to be given to 'grey' areas where considerable caution in the interpretation of comparisons is advisable, and on topics where comparison though possible is inadvisable.

User views or requirements

How did users of Census 2001 data use or develop applications for comparisons with previous Census data?

What are the important lessons we can we learn from and implement for dissemination and analysis of 2011 / 2001 data comparison?

In situations where the quality and integrity of comparsions becomes unnaceptably low (becuase of intercensal or other changes) or comparisons cannot be made (becuase of disclosure or other issues) there are a number of was to mitigate the scale and intensity of these instances, and to improve the overall utility of the data, such as:
1. replace

What are the most useful / used variables in comparison analysis?

Issues relating to differences in methodology and from other changes between censuses

geography (Output Areas, administrative geography)
changes in questions asked, or in the interpretation of question meaning by respondents
population base

*updating 2001 definitions

output classifications
other methodology
disclosure routines
choice of optimum 2001 count for use in comparison when count definition is replicated accross tables but with slightly varying values

Disclosure control - differences and effects