Modifiable areal unit problem
The modifiable areal unit problem (MAUP) is a source of statistical bias that can radically affect the results of statistical hypothesis tests. It affects results when point-based measures of spatial phenomena (e.g. population density) are aggregated into districts. The resulting summary values (e.g. totals, rates, proportions) are influenced by the choice of district boundaries. For example, census data may be aggregated into census enumeration districts, or postcode areas, or police precincts, or any other spatial partition (thus, the "areal units" are "modifiable").
The issue was discovered in 1934 and described in detail by Openshaw (1984), who lamented that "the areal units (zonal objects) used in many geographical studies are arbitrary, modifiable, and subject to the whims and fancies of whoever is doing, or did, the aggregating."
See also 
- General topics
- Specific applications
- Gehlke and Biehl (1934)
- Openshaw (1984, p. 3)
- Cressie, N. (1996). "Change of Support and the Modifiable Areal Unit Problem." Geographical Systems, 3:159-180.
- Gehlke, C. and Biehl, H. (1934). Certain effects of grouping upon the size of the correlation coefficient in census tract material. Journal of the American Statistical Association Supplement, 29, 169–170. doi:10.2307/2277827
- Holt D, Steel D, Tranmer M, Wrigley N. (1996). "Aggregation and ecological effects in geographically based data." Geographical Analysis 28:244–261.
- Openshaw, S. (1984). The Modifiable Areal Unit Problem. Norwich: Geo Books. ISBN 0-86094-134-5.
- Unwin, D. J. (1996). "GIS, spatial analysis and spatial statistics." Progress in Human Geography. 20: 540-551.