“General requirements for the competence of testing and calibration laboratories” (commonly referred to as “ISO 17025”), which includes a well-established list of techniques that can be used, alone or in combination, to validate a method:
calibration using reference standards or reference materials;
comparison of results achieved with other methods;
systematic assessment of the factors influencing the result; and
assessment of the uncertainty of the results based on scientific understanding of the theoretical principles of the method and practical experience.1
A critical step in such validation studies is their publication in peer-reviewed journals, so that experts in the field can review, question, and check the repeatability of the results. These publications must include clear statements of the hypotheses under study, as well as sufficient details about the experiments, the resulting data, and the data analysis so that the studies can be replicated. Replication will expose not only additional sources of variability but also further aspects of the process, leading to greater understanding and scientific knowledge that can be used to improve the method. Methods that are specified in more detail (such as DNA analysis, where particular genetic loci are to be compared) will have greater credibility and also are more amenable to systematic improvement than those that rely more heavily on the judgments of the investigator.
The validation of results over time increases confidence. Moreover, the scientific culture encourages continued questioning and improvement. Thus, the relevant scientific community continues to check that established results still hold under new conditions and that they continue to hold in the face of new knowledge. The involvement of graduate student researchers in scientific research contributes greatly to this diligence, because part of their education is to read carefully and to question so-called established methods. This culture leads to continued reexamination of past research and hence increased knowledge.
In the case of DNA analysis, studies have evaluated the precision, reliability, and uncertainties of the methods. This knowledge has been used to define standard procedures that, when followed, lead to reliable evidence. For example, below is a brief sample of the specifications required by the Federal Bureau of Investigation’s (FBI’s) Quality Assurance Standards for