### Abstract

When, in a criminal case there are traces from a crime scene - e.g., finger marks or facial recordings from a surveillance camera - as well as a suspect, the judge has to accept either the hypothesis \emph{$H_{p}$} of the prosecution, stating that the trace originates from the subject, or the hypothesis of the defense \emph{$H_d$}, stating the opposite. The current practice is that forensic experts provide a degree of support for either of the two hypotheses, based on their examinations of the trace and reference data - e.g., fingerprints or photos - taken from the suspect. There is a growing interest in a more objective quantitative support for these hypotheses based on the output of biometric systems instead of manual comparison. However, the output of a score-based biometric system is not directly suitable for quantifying the evidential value contained in a trace. A suitable measure that is gradually becoming accepted in the forensic community is the Likelihood Ratio (LR) which is the ratio of the probability of evidence given \emph{$H_p$} and the probability of evidence given \emph{$H_d$}. In this paper we study and compare different score-to-LR conversion methods (called calibration methods). We include four methods in this comparative study: Kernel Density Estimation (KDE), Logistic Regression (Log Reg), Histogram Binning (HB), and Pool Adjacent Violators (PAV). Useful statistics such as mean and bias of the bootstrap distribution of \emph{LRs} for a single score value are calculated for each method varying population sizes and score location.

Original language | English |
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Title of host publication | 33rd Symposium on Information Theory in the Benelux and the 2nd Joint WIC/IEEE Symposium on Information Theory and Signal Processing in the Benelux 2012 |

Place of Publication | Enschede |

Publisher | Werkgemeenschap voor Informatie- en Communicatietheorie (WIC) |

Pages | 126-133 |

Number of pages | 8 |

ISBN (Print) | 978-90-365-3383-6 |

Publication status | Published - May 2012 |

Event | 33rd WIC Symposium on Information Theory in the Benelux and the 2nd Joint WIC/IEEE Symposium on Information Theory and Signal Processing in the Benelux 2012 - Boekelo, Netherlands Duration: 24 May 2012 → 25 May 2012 Conference number: 33 |

### Conference

Conference | 33rd WIC Symposium on Information Theory in the Benelux and the 2nd Joint WIC/IEEE Symposium on Information Theory and Signal Processing in the Benelux 2012 |
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Country | Netherlands |

City | Boekelo |

Period | 24/05/12 → 25/05/12 |

### Keywords

- METIS-287889
- EWI-21962
- SCS-Safety
- IR-80693

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## Cite this

Ali, T., Spreeuwers, L., & Veldhuis, R. (2012). A review of calibration methods for biometric systems in forensic applications. In

*33rd Symposium on Information Theory in the Benelux and the 2nd Joint WIC/IEEE Symposium on Information Theory and Signal Processing in the Benelux 2012*(pp. 126-133). Enschede: Werkgemeenschap voor Informatie- en Communicatietheorie (WIC).