1. Department of Mathematics, University of Waikato, Hamilton 3216, New Zealand;
2. New Zealand Institute of Security and Crime Science, Hamilton 3216, New Zealand;
3. Department of Computer Science, University of Waikato, Hamilton 3216, New Zealand;
4. School of Psychology, New Zealand Institute of Security and Crime Science, University of Waikato, Hamilton 3216, New Zealand;
5. Department of Statistics, University of Auckland, Auckland 1142, New Zealand