Q: The population of my parish is shown as rising steadily over several censuses but then suddenly falls. Was this because they all died in an epidemic?

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A: Maybe, but it is more likely that the boundary changed. Our historical statistics for modern districts have been "redistricted", so they always cover the same geographical area. However, all other statistics are reported for the relevant unit as it was defined by the relevant census, or other statistical report. Big boundary changes therefore create big apparent changes in the statistics. The system also holds systematic information on boundary changes, so you can work out if these were a factor. We also often hold data on the total population of the current area at the previous census; for example, the figure the 1911 census reported as the area's population in 1901. If this is very different from the total population reported by the 1901 census, you can be certain that major boundary changes were happening.

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