Typically, in medical journals, we don’t like to include a lot of formula or mathematical expressions in articles. However I recently read a paper where a mathematical expression is used to describe the COPD as a syndrome. It is a good use of mathematical expression in this case.
John J. Reilly “COPD and declining FEV1 – time to divide and conquer?” (NEJM 359:15: 1616-1618 OCT 2009)
“In fact, COPD in the singular is probably a misnomer. It is more appropriate to view COPD as a syndrome that encompasses a variety of obstructive diseases that share a common exposure but differ in terms of mechanism of disease and response to therapy. This concept is expressed in the mathematical notation
In which COPDn represents subgroups of COPD. As a reflection of this recognized heterogeneity, investigator have developed new classification systems, such as the BODE index, which evaluates the body-mass index, the degree of airflow obstruction and dyspnea, and exercise capacity to create a 10-point scale in which higher scores indicate a higher risk of death. In addition, investigators have attempted to define other homogeneous subgroups of patients with COPD. “
For many complicated diseases, when we have a better understanding about the disease, we will see that one specific disease may have many different manifestations or phenotypes – so called ‘heterogeneity’. When designing a clinical trial for a disease with heterogeneity, it may be difficult to show the treatment effect on the patient population as a whole. The drug may only be effective on one of many specific sub-populations. The difficult is usually in finding this specific sub-population. The newly issued FDA guidance “Enrichment Strategies for Clinical Trials to Support Approval of Human Drugs and