14. Developing an automatic matching system for court dates
14.2 An outline of an operational system
With the above work, an outline of a proposed classification system can be proposed. We describe the system as though a set of names have been presented to RDS as part of a research study (Figure 2.1)
1. For every offender under study, trace the offender on the PNC and the OI and obtain the criminal histories. 2. Exclude non England and Wales convictions from the PNC if this is desired.
3. For every distinct court date on the PNC and on the OI, calculate the number of standard list offences in each of the ten Criminal Statistics categories. Also calculate the smallest court code and police code used for that court date.
4. For each court date on the Offender Index, calculate the logit score to every court date with a court conviction on the PNC. Accept the PNC court date record with the highest logit score as a match if the score is above zero, otherwise treat the court date as unmatched. Flag the PNC record which has been matched as taken, and do not consider it for subsequent matching for this offender.
5. Merge in all unmatched PNC records, including all unmatched court convictions, and all records relating to non-court disposals.
6. (Optionally) manually examine all offenders with low match rates (less than 50%) to see if there is evidence of split records on the OI which need demerging.
It remains to be seen how this procedure performs in practice. If more time were available, this would be the next stage of the research project. In particular, Stage 4 of the above procedure may be too time consuming and other less exact methods may be acceptable.
We recommend that RDS pilots the above procedure and evaluates it on new and existing datasets. This will again need purpose written software to be constructed.
A final problem when matching records is that it is easy to obtain a hybridised record with contradictory information in the PNC half and the OI half of the record. Which information should be taken? This needs further investigation – our provisional thoughts are that:
• Individual level fields such as gender and date of birth should be reconciled where possible. It is however likely that the PNC contains more accurate data.
• Differences in court dates matter less if date of offence is to be used as the outcome measure in reconviction studies. It is likely that the OI as the primary source contains more accurate information.
• Contradictory information is likely to exist in the number and type of offences. Both PNC and OI data are likely to be reliable – the advice here is to choose the OI information if standard list offences are required and PNC if all offences are needed.
Acknowledgements
The authors are grateful to Philip Howard and Julian Prime, who commissioned this research and who provided much helpful guidance and encouragement throughout the research. At Lancaster, Juliet Harman dealt with the preparation, recoding and analysis of the data studies and we are particularly grateful for her skill, accuracy and dedication. We also thank Jayn Pearson, who has worked tirelessly in carrying out the majority of the matching work.
References
Allnutt, D (2001) Review of Statistics on Efficacy of Sentencing. Office of National Statistics, London
http://www.statistics.gov.uk/themes/yourviews/downloads/postconsdrft.pdf
Colledge, M., Collier, P. and Brand, S. (1999). Programmes for Offenders: Guidance for Evaluators. Crime Reduction Programme, Guidance Note 2, London: Home Office.
Copas, J. and Marshall, P. (1998). 'The Offender Group Reconviction Scale: the statistical reconviction score for use by Probation Officers.' Journal of the Royal Statistical Society, Series C, 47, 159-171.
Crosland, P. (1999) Report on Offenders' Index and Police National Computer Data for the Strategic Alliance Steering Group (unpublished)
Crosland, P. and Rex, S. (2001) The Strategic Alliance Probation Areas Reconviction Study, Herts, Northants, Beds and Cambs Probation Services.
Dodgson. K et al. (2001) . Electronic monitoring of released prisoners: an evaluation of the Home Detention Curfew scheme. Home Office Research Study No 222, London: HMSO.
Friendship, C.et al (2000) Reconviction: a critique and comparison of two main data sources in England and Wales (submitted to Legal and Criminological Psychology, March 2000)
Home Office (2000) Criminal Statistics, England and Wales 1999. London:HMSO
Howard, P. and Kershaw, C. (2000) Using Criminal Career Data in Evaluation in Mair, R. and Tarling (2000) The British Criminology Conference: Selected Proceedings. Volume 3. Papers from the British Society of Criminology Conference, Liverpool, July 1999.
Kershaw, C. et al (1999) Reconvictions of offenders sentenced or discharged from prison in 1995, England and Wales. Home Office Statistical Bulletin 19/1999
Lloyd, C., Mair, G. and Hough, M. (1994) Explaining Reconviction Rates: A Critical Analysis. Home Office Research Study No 136, London: HMSO.
Newcombe, H.B. (1988) Handbook of Record Linkage. Oxford University Press, Oxford
Police Information Technology Organisation (2000) Phoenix System Data Definitions Version 3.23. Police National Computer Directorate.
Povey, K (2000) On The Record –Thematic Inspection report. Police crime recording, the Police National Computer, Phoenix Intelligence System Data Quality Her Majesty’s Inspectorate of Constabulary, London.
Prime, J. et al. (2001) Criminal careers of those born between 1953 and 1978 Statistical Bulletin 4/01 London: Home Office.
Rose, G, (2000) The Criminal Careers of Serious Traffic Offenders Home Office Research Study No 206, London: HMSO.
Russell, J. (1998) Phoenix Data Quality. Special Interest Series: Paper 11. London: Police Research Group.
Soothill, K., Francis, B., Ackerley, E. and Sanderson, B. (2000). Sex offenders: specialists, generalists or both?: a 32- year criminological study. British Journal of Criminology, 40, 56--67.
Tendler, S (2001) Records chaos may put police chiefs in court The Times, 14th April, p15.
Wain, R, Francis, B and Stott, D. (1993) Software for routine record linkage in public health In: Healthcare Computing 1994 (Ed. Richards, B) pp 681-688. ISBN 948198 17 6