Chainey, S

Tompson, L

Uhlig, S

English

UCL Discovery

This is a pre-print of a commentary accepted for publication by the Security Journal in 2008. It is a pre-copy-edit version of the letter that is found at http://www.palgrave-journals.com/sj/journal/v21/n4/abs/sj20088a.html   Response to Pezzuchi 2008, ‘A Brief Commentary on "The Utility of Hotspot Mapping for Predicting Spatial Patterns of Crime"’.  Security Journal.  Spencer Chainey¹, Lisa Tompson², and Sebastian Uhlig³  1  Director  of  Geographical  Information  Science,  Jill  Dando  Institute  of  Crime  Science, University College London, Brook House, 2-16 Torrington Place London. WC1E 7HN 2 Research Fellow, Jill Dando Institute of Crime Science, University College London, Brook House, 2-16 Torrington Place London. WC1E 7HN 3  Project  Consultant,  Informed  Solutions,  The  Old  Bank,  Old  Market  Place,  Altrincham, Cheshire. WA14 4PA, UK  Gaston Pezzuchi raises some useful points for consideration.  In reply,   We  acknowledge  that  there  are  other  techniques  that  can  be  used  for hotspot mapping, but as we state in the opening section of the paper we chose to test against techniques that were well known and had been in popular use for some time.  Hence our decision to include the STAC spatial ellipses  technique,  using  CRIMESTAT  to  generate  the  results  from  this method.    We  also  acknowledge  that  there  are  other  techniques  that generate ellipses, but for sake of brevity we only refer to ‘spatial ellipses’ throughout the paper after making clear reference in an opening section that the particular technique we were referring to was STAC.   By reporting on the results from what we considered were the most popular techniques and explaining the methodology we applied we hoped that this would encourage others to repeat the experiments for other techniques.  We are aware that since the paper has been published others are indeed applying  our  methodology  to  compare  results  generated  using  nearest neighbour hierarchical clustering techniques.  We hope that they too will publish their findings.   We  acknowledge  that  there  are  differences  between  cluster  detection techniques and other representation methods.  Our paper, however, was not  solely  about  cluster  detection  techniques  but  was  about  hotspot mapping techniques that generally, in practice, include both.   We apologise for the confusion we may have generated when explaining the thematic mapping techniques.  These are indeed choropleth maps, and we point the reader in our paper to a number of references that describe these techniques in more detail.  We felt it unnecessary to repeat this detail in the paper.   We did not intend to offer any bias towards the Hotspot Detection software solution.  The kernel density estimation (KDE) algorithm that it uses is the same as that for generating KDE maps in CRIMESTAT.  We merely used Hotspot Detective because it is a software solution that is in common use and  because  it  provides  the  user  with  default  values  for  cell  size  and bandwidth.  CRIMESTAT does not offer similar defaults for testing.   One  solution for deciding  upon  a  suitable KDE  bandwidth  is to  use  the adaptive bandwidth approach.  The research we reported on applied the more common (in practice) method of a fixed bandwidth (e.g. using the default  bandwidth  in  Hotspot  Detective  or  by  entering  in  the  bandwidth following  guidance  reported  in  other  research).    We  have  completed additional research that fully tests the impact of bandwidth and cell size on KDE results and intend to publish these.  We also intend to repeat our methodology  using  a  KDE  adaptive  bandwidth  approach,  but  also encourage others to repeat our methodology using this approach too.   The  quantile  approach  for  determining  thematic  threshold  values  was chosen  because  it  is a  common  range  method  that  is used  in  practice.  However, it is not without its problems and we encourage others to repeat our methodology using other thematic range methods and publish these results.   Without  providing  specific  details  we  are  not  certain  what  the  other concerns are with the “forecasting power, the temporal variable and similar things”.  However, we do encourage others to strengthen and add to the research we have reported on by using the paper as a foundation for them to develop additional research on the subject.  We are encouraged by the debate the paper has generated and on reports that many have found the results useful and a basis on which to test other techniques. 

A Brief Commentary on "The Utility of Hotspot Mapping for Predicting Spatial Patterns of Crime" Response

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