Firstly how did I create the map?
- I downloaded the neighbourhood data for all the forces (unfortunately the Sussex spreadsheet was empty) and created a force total of the five categories of crime and one category of anti-social behaviour for December 2010.
- I attempted to compensate for the different sizes of the forces by dividing the counts in the six categories by the latest published total police officer and staff numbers for each force. This has its problems (and benefits which I will argue elsewhere) but it is better in my opinion than dividing by resident population.
- I then wanted to cluster the data giving equal weight to each category (see my previous posts regarding clustering) so I standardized all the data by transforming them into Z scores. This shows the standard deviation either side of the mean creating positive and negative figures.
- I then decided the best probable number of clusters by using the Ward's Hierarchical method in SPSS 17 and choose 6. I then used the K means clustering method with the six clusters.
- The K means method allows a better understanding of what factors has influenced the clustering, allowing a classification of the clusters to be reliably undertaken. This classification is shown under the map above with a table showing the scores for the cluster centres.
- Now this is where I need help. I cannot find a shapefile for police forces in England and Wales. Edina has a shapefile for police force basic command units for England and a seperate one for Wales. I had to do a bit of editing to the .dbf file to show my classification at force level using ArcGIS.
But what are the data I am classifying and mapping here?
To be honest you I do not know, I could find no documentation to explain. Now I am assuming that the crimes are police recorded crime in Home Office Crime Types but it would not surprise me to find out that there have been problems in ensuring that every force is submitting exactly the same types of crime. The chances of that being uniformly the same is a lot higher than the Anti-Social Behaviour figures, which I am assuming are from the police incident recording database and would not surprise me if they differ significantly in content from force to force.
So that is the number one fundamental problem - what is being counted, how is it counted and is it the same through out the country?