Given the probative value which tribunals may assign to expert witness evidence, their role has been restricted to instances where their expertise is unavoidably necessary. However, as fields of scientific knowledge continue to expand, and with the advent of forensic evidence, such instances are now commonplace, and the need for experts has been described as 'ever-expanding'.[3] Common areas that expert witnesses offer opinion on are ballistics, blood-alcohol calculations and levels, DNA or genetic fingerprinting, and fingerprint identification. Such areas are the least controversial, as the expert is testifying on science which is generally accepted, and their opinion will, in the absence of fraudulent process, be reproducible by other experts.