Final answer:
The MDRD does not define the period for which obsolete controlled documents should be retained; this is typically outlined by regulatory requirements or a company's quality management system, not a medical study equation like the MDRD.
Step-by-step explanation:
The requirement for the MDRD (Modified Diet in Renal Disease) to define the retention period for at least one copy of obsolete controlled documents is generally not true. The MDRD Study Equation is related to medicine and specifically to the estimation of kidney function. However, the question seems to be conflating this with document retention policies, which are typically governed by a company's quality management system (QMS) or regulatory requirements in various industries. For instance, in pharmaceutical or medical device industries, regulations like those from the FDA (Food and Drug Administration) or ISO (International Organization for Standardization) may dictate how controlled documents should be managed, including the retention of obsolete versions.
Document retention policies, including those for obsolete documents, are crucial for maintaining historical data for reference in case of audits or to understand the evolution of processes and products. The specifics of such policies would depend on the industry and the specific regulatory requirements it needs to adhere to. Depending on the context, regulations might require the retention of documents for a specific period, often several years after the document has been superseded or become obsolete.