Geographical Units
There are three main choices of geographical unit for small area analysis (in descending order of average population size):
- Postcode sectors: There are 1,010 postcode sectors in Scotland. A postcode sector is identified by omitting the last 2 characters of the full postcode (e.g. KA23 9, FK8 3, G2 9). The average population in the 2001 census was 5,012, but it varied from 53 in the smallest sector to 20,455 in the largest. Note that postcode sector population estimates have not been available since 2000.
- Data Zones: These are designed to represent neighbourhoods. There are 6,505 data zones, and they are comparatively homogenous in size with an average population size of 798 in 2009. The smallest non-zero data zone represents 212 people and the largest 7,061 people.
- Output areas: These are the smallest geographical unit for which Census data are available. There were 42,604 output areas at the 2001 Census with a mean population size of 119 people. The smallest output area represents 50 people and the largest represents 2,357 people. This wide variation is due to a few large output areas with populations in communal establishments.
Pockets of deprivation are best identified using as small geographical units as possible, so other things being equal, the use of output areas should be the favoured choice. However, the 1981 and 1991 Carstairs indices are only available for postcode sectors. The 2001 Carstairs indices are available for postcode sector, data zone and output areas. The SIMD is available for data zones.
Deprivation Categorisation
There are four main categories:
- 7 Categories have previously been used in ISD to split the population. The categories are of unequal size and the most and least deprived groups include the smallest populations. For statistical analysis it is desirable to have equally-sized groups so ISD have now moved away from this categorisation.
- Deciles used within ISD divide the population into ten equal categories so that 10% of the population falls into each decile (population weighted). Deciles have been calculated at Scotland level and also within individual health boards. Note : Following the release of the SIMD 2009 ISD have changed their ordering of deciles to fit with the method that is used by the Scottish Government (SG). The method is now:
1=MOST deprived
10=LEAST deprived
and applies to all data analysed by SIMD 2009.
Note: Any SIMD analyses based on SIMD 2006 or SIMD 2004 already published on the ISD website (and any further analyses done using SIMD 2006 or SIMD 2004) will be left in their current format i.e. 1=LEAST deprived, 10=MOST deprived. - Quintiles used within ISD divide the population into five equal categories so that 20% of the population falls into each quintile (population weighted). Quintiles have been calculated at Scotland level and also within individual health boards. Note : Following the release of the SIMD 2009 ISD have changed their ordering of quintiles to fit with the method that is used by the Scottish Government (SG). The method is now:
1=MOST deprived
5=LEAST deprived
and applies to all data analysed by SIMD 2009.
Note: Any SIMD analyses based on SIMD 2006 or SIMD 2004 already published on the ISD website (and any further analyses done using SIMD 2006 or SIMD 2004) will be left in their current format i.e. 1=LEAST deprived, 5=MOST deprived. - Top and bottom 15% relate to National targets being set by the Scottish Government Health Department which will be based on the 15% most deprived and 15% least deprived.
