"As prediction methods find more use and our experience increases, the refinement of prediction instruments and the increase of prediction accuracy can be expected to develop rapidly."
Fig.1. Results of Ohlin's 1951 study, data taken from p.130 of Ohlin (1951)
1 - Ohlin, S.E. 1951. Selection for Parole. Russell Sage Foundation, New York.
2 - Simon, F.E. 1971. Prediction Methods in Criminology. H.M. Stationary Office, London.
3 - The Mean Cost Rating is a statistic that describes the effectiveness of a predictor, taking into account the weights of the various items.
In the 1950's and 60's the government carried out a number of studies, as part of a review of the effectiveness of the probation service in preventing re-offending. One study that formed part of the Home Office Probation Research Project was aimed at designing an accurate statistical predictor of re-offending. This was to allow a balanced comparison of the effectiveness of different probation regimes. The study was carried out by Simon (1971).
Simon based his instrument on 62 objective items of information that described the probationer's personal or criminal history. All these items could be found in government or case records, although not all had any apparent relevance to the likelihood of re-offending. The criterion for failure was re-conviction of a Standard List offence within three years of the probation order commencing. Simon's sample consisted of 539 young men between the ages of 18 and 21, who all began probation orders in 1958. Simon carried out 17 predictive analyses on the data using a variety of methods and selections of the 62 variables. Most of these analyses produced a predictor of moderate power on construction, but almost all shrank considerably on validation. The most successful predictive analysis was a Predictive Attribute Analysis which produced a predictor with an M.C.R. of 0.45 on construction, which shrank to 0.25 on validation. When the predictor was applied to a fresh set of data in 1964 it achieved an M.C.R. of 0.18 on construction, that shrank to 0.9 on validation.
These results are considerably lower than one would expect following a review of earlier studies. Vold (1931) recorded Correlation Coefficients of over 0.2 for several individual items, including criminal record, marital status, social type, and previous work record. Vold's most successful predictor achieved an M.C.R. of 0.71 on validation. This would appear exceptional, but many others have designed predictors that have achieved M.C.R.'s of between 0.3 and 0.4. Ohlin (1951) produced a predictor that achieved 0.36 on validation, and this score was matched by Glaser (1962).
Simon concluded that his poor results were largely the result of a sample that was not large enough to identify genuine trends, and reject co-incidental relationships, and that as such considerable shrinkage occurred on validation, this seems to be the case. For example one item, the age of offender at the time of a break or disturbance in his domestic arrangements, showed a predictive relationship of P<.001 on construction, this relationship vanished to P>.05 on validation. The sample size certainly seems small in comparison with earlier studies. Vold (1931) used a sample of 1,192, Glaser based his study on a sample of 2,637, and Ohlin examined data from 17,097 offenders. Simon concludes pessimistically about the potential usefulness of prediction studies, saying,
"the study shared the general fate of criminological prediction studies...although small groups of good or bad risks could be distinguished, for many of the cases little discrimination is achieved."
The Home Office again had cause to need an efficient prediction instrument for re-offending when it introduced parole in 1968. On this occasion the study was carried out by Nuttal et al, and is detailed in Nuttal et al (1977)(1). It would appear the C.P. Nuttal and his team learnt the lessons of Simon's failure. They based their predictor on seventeen items that were easily accessible from administrative records, and that had consistently shown predictive power in previous studies. Their sample was of 2,276 male prisoners released from prison in the first six months of 1965. The criterion for failure was re-conviction within two years of release. The results of this study were very encouraging, with the predictor achieving an M.C.R. of 0.5 on construction that expanded to 0.557 on validation, see fig.2. As Nuttal concludes, this study appears to show that,
"by using a large sample...an efficient instrument could be devised for predicting the likelihood of re-conviction among medium and long-term prisoners."
Fig.2. Results of Nuttal et al's 1977 study, taken from Nuttal et al (1977)(1)
1 - Nuttal, C.P. et al. 1977. Parole in England and Wales. H.M. Stationary Office, London.
Whilst Nuttal's study was successful in the context of prediction studies in general, it was still a long way from being 100% accurate. There is a ceiling on how accurate a prediction instrument can be because a predictor can only take into account factors that are measurable at the time that the predictor is applied. In the case of re-conviction, factors such as attitude to authority and motivation to remain within the law, which may have predictive power, are almost impossible to measure, especially if an offender believes that these factors will influence their release date. Other factors that play a significant role in determining whether an offender remains within the law only come into play upon their release. These 'environmental factors' include such things as a supportive family, a law-abiding social group, and a regular job.
Davies (1969) examined the role of such environmental factors in a study(1) that was part of the Home Office Probation Research Programme. Whilst Davies' intention was not to predict re-offending, he recorded a 'stress score' for those who participated in his study. This stress score was based on a number of environmental factors that he speculated would have a detrimental effect on the probationer's chances of success. The stress score had considerable predictive power, achieving an M.C.R. of 0.24. This is significant because the stress score was not the most powerful instrument that could be derived from the data, and several of the factors included proved to have little predictive power, weakening the instrument as a whole. The relationship between the stress score and the failure rate can be found in fig.3.
Stress Score No. Failing Failure Rate
0 25 .26
1 40 .33
2 40 .31
3 36 .48
4 & 5 37 .56
6 & 7 11 .61
Fig.3. - The relationship between the stress score and the failure rate. Taken from Davies (1968), Table 9.4.
The findings of Lohman et al in the San Francisco Project seem to support Davies' finding that environmental factors have a strong influence on the chances of avoiding re-conviction. Lohman et al found that parolees who had successfully completed their parole attributed their success to environmental factors. It is important not to read too much into these findings, as Nuttal and Lohman were not explicitly investigating the role of environmental factors.
1 - Davies, M. 1969. Probationers in their Social Environment. London: H.M. Stationary Office.
Simon (1971) argues that such 'environmental' factors, as well as a small sample, were a factor in the failure of his study. One other possible reason for his failure that he does not discuss is the age of his chosen sample. The average age of an offender is 20(1), this would seem to indicate that most crimes are committed by young people. Clearly not all these individuals go on to become career criminals. It therefore follows that the 18-21 age range is critical for young offenders because at this time they either settle down to a normal life, or continue as recidivists. The work of Davies seems to indicate that environmental factors are significant in determining whether an individual adopts a life of crime. The work of Simon on the other hand seems to show that the probationer's personal or criminal history has relatively little impact whether the individual will go on to re-offend.
Nuttal et al conducted their study on adult prison inmates, and their results show that an offender's personal or criminal history are powerful predictors of re-offending. A possible explanation for this is that, whilst environmental factors are significant for young probationers, they are relatively insignificant for adult offenders. If detrimental environmental factors are a significant factor in leading an individual to a life of crime, then by adulthood those vague environmental factors will be evidenced in the individuals criminal record. This could explain why Nuttal's study was so successful. However such a comparison between the studies of Simon and Nuttal is complicated by the differences in method. Therefore, as a theory, this can be no more than informed speculation. A study in which identical measures of both personal and criminal history, and environmental factors, are applied to both young probationers and adult criminals would help to establish the relationship between environmental factors and age.
In conclusion then I would argue that it is possible to predict whether adult offenders will re-offend with a fair degree of success, simply by analysing their personal and criminal history. When attempting to predict whether young people will be re-convicted however, it is important to attempt to include some measure of the environmental factors that the individual will face when they are released.
1 - Bottomley, K. & Pease, K. 1986 Crime and Punishment - Interpretting the Data. Open University Press: Milton Keynes.
References
Borden, H.G. 1928 "Factors for Predicting Parole Success." Journal of American Institute of Criminal Law and Criminology, 19: 328-36.
Bottomley, K. & Pease, K. 1986 Crime and Punishment - Interpretting the Data. Open University Press: Milton Keynes.
Burgess, E.W. 1942 "Rejoinder." American Journal of Sociology, 48: 84-86.
Davies, M. 1969. Probationers in their Social Environment. H.M. Stationary Office: London.
Hamlin, R. 1934. "Predictability of Institutional Adjustment of Reformatory Inmates." Journal of Juvenile Research, 18: 179-84.
Meehl, P.E. 1954. Clinical v. Statistical Prediction: a theoretical analysis and review of the evidence. University of Minnesota Press: Minneapolis.
Nuttal, C.P. et al. 1977. Parole in England and Wales. H.M. Stationary Office: London.
Ohlin, S.E. 1951. Selection for Parole. Russell Sage Foundation: New York.
Schiedt, R. 1936. Ein Beitrag zum Problem der Ruckfallsprongnose. Ph.D. thesis. Munich: Munchner-Zeitungs-Verlang
Simon, F.E. 1971. Prediction Methods in Criminology. H.M. Stationary Office: London.
