Medical tests to determine ones age actually give only an estimate in terms of an age range. And the younger the person whose age is being estimated, the higher the likelihood of accuracy, say forensic experts.
Such tests, used to settle uncertainty over someones age when documentary proof is not available, will now seek to establish the claim of one of the accused in the Delhi bus rape. He says he is short of 18 by a few months, which if established would make him a minor.
Usually a medical board is set up, which includes a general physician, a dentist, a radiologist and a forensic expert, says Dr R K Sharma, former head of forensic medicine at AIIMS and editor of the Indian Journal of Forensic Medicine and Toxicology.
A bone test or ossification is one of the tests and involves analysis of the bones on an X-ray, Dr Sharma says. Dental X-rays too are taken, besides a thorough physical examination of the person that includes an analysis of secondary sexual characteristics. After a cumulative analysis of all the tests, the age is declared.
He added the bone test is usually regarded as the most conclusive among all these examinations. It involves X-rays of all major limb bones, including pelvic, shoulder, elbow, knee, ankle, thigh and wrist.
At birth, most of the middle part of the bone, known as the shaft, is bony tissue, and the ends are cartilaginous, says Dr Sreenivas, associate professor of forensic medicine at Maulana Azad Medical College. As a person grows and goes through puberty, the cartilaginous portions are converted to bone tissue. Every bone completes this process at a specific age, which is defined in forensic textbooks. This conversion is a process known a ossification.
An estimation of ones age, therefore, involves a study of the progress of ossification in the bones. It is a good method, with a fair deal of accuracy in estimating age, though there are limitations. We can only give the age within a range of two to three years. Giving the exact age is not possible, says Dr Harsh Mahajan, president of the Indian Radiology Association. In children where we do not want to subject the child to radiation, we sometimes do an MRI instead of an X-ray.
Forensic experts say the accuracy of the age estimate is inversely proportional to the age of the person.
When a person is young, within the growing