Locating communities in Blackburn

In order to locate suitable areas for interviews and filming, Panorama commissioned a number of images such as the one below.

Onto this image were placed a number of coloured symbols. These symbols indicate the proportion of the adults estimated to be of Pakistani or Bangladeshi origin or descent.

The red circles on the map of Blackburn indicate postcodes where, according to Experian, in 2006 over 75% of adults are of Pakistani or Bangladeshi descent. These form the core heartlands of Blackburn's Muslim community.

Surrounding these areas are yellow circles which indicate other postcodes where Muslims now form the majority population. It is in these areas that the Muslim community is currently purchasing the homes of the minority of white residents who still live there.

Map showing the population spread in Blackburn

By contrast the blue squares, which show postcodes where Muslims represent between a quarter and a half of the adult population, denote streets where the transition from white to Muslim is likely to be accelerating.

The light blue triangles denote parts of Blackburn that are still predominantly white in character and which are likely to remain so over the next ten years.

Traditionally researchers have had to rely on the census to identify the size and location of different minority groups.

Though the census has many benefits, the growth and spread of Blackburn's Muslim community since the last census in 2001, means that its results are out of date.

Likewise because the smallest geographical pieces for which census statistics are published are so much larger than individual postcodes, census based mapping can not provide the level of detail needed by Panorama to examine what is going on on a street by street basis.

To create and update their statistics Experian first compiled a register of all known UK adults at their home address.

This was created using the electoral register and a number of other public and private data sources. Using a look up table that assigns "origin" codes to over one million of the world's family names and over 450,000 personal names, they were able to impute an "origins" code for 99.9% of the names on their file.

It is the summary of this information at the postcode level that provides the information that is shown on the map.

Clearly not every resident can be identified from his or her name with 100% accuracy.

However by using both personal and family name, it is possible to identify whether a person is of Pakistani or Bangladeshi origin with an accuracy in the region of 95%. Once this information is summarised at postcode level these errors tend to be self-cancelling.

Panorama: White Fright will be broadcast on Monday 7 May at 2030 BST on BBC One.

Or watch online on the Panorama website

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