After determining that a fragment of glass is indistinguishable from a window at a crime scene, the glass examiner is then faced with the task of assessing the significance of this result and providing that significance measure to the interested parties. There are two approaches that can be used for this. Some glass examiners will determine that two samples are indistinguishable based on refractive index (RI) and then use a database of RI values to obtain the frequency of occurrence of glass having the particular RI in question. Other glass examiners may use the likelihood ratio approach in which they use databases of RI values to determine the relative probabilities of competing hypotheses as to the origin of a questioned fragment of glass. In either approach, it is essential that the glass examiner have access to an accurate database containing RI values determined from appropriate, representative samples.
