An Assessment of Intra- and Interobserver Error in Luminol Chemiluminescence as a Presumptive Test for Postmortem Interval Estimation

Abstract

Postmortem interval (PMI) estimation constitutes a challenge for forensic anthropologists. The application of the luminol technique as a preliminary test for PMI estimation is considered easy to use and inexpensive. The objective of our study is to validate luminol chemiluminescence testing through the assessment of intra- and interobserver error. Our sample included 266 human clavicles, with known PMIs ranging between 2655 days and 450 years. After sample preparation, luminol was applied, and the results were observed by two different observers. The intensity of the reaction was measured using a binary scale and a 5-level scale, according to the increasing degree of chemiluminescence. The Kappa statistic was used for the assessment of the intra- and interobserver agreement. The obtained results showed total interobserver error agreement regarding the binary scale and a K = 0.98 (95% CI: 0.97–0.99) regarding the 5-level scale. Additionally, Observer 1 and Observer 2 obtained a 100% agreement concerning the binary scale and a K = 1 (95%CI 0.99–1) and K = 0.99 (95% CI 0.99–1), respectively, concerning the 5-level scale. According to our research, it is possible to conclude that luminol chemiluminescence testing is suitable as a rapid diagnostic test, revealing this method as practically independent of observation error.