Rank drift, rank inflation or rank deflation refers to the situation where a rank no longer represents the strength it used to, or conversely, a ranking or rating system, assigns a different rank or rating than previously to a player of the same strength. When a given rank represents a lower standard than it used to, this is referred to as rank inflation: the rank loses its value, as happens to money during inflation. When a given rank represents a higher standard than it used to, we speak of rank deflation.
When drift occurs in a ranking system, the problem is usually solved by recalibrating the ranks; this may need to happen regularly or continuously. This solution is most common for online go servers. Most professional organizations do not rebalance older rankings, but instead change how newer rankings are gained in future events. This can often lead to a clear demarcation in ranks between generations of players. It also makes it easier for researchers and policy makers to observe and study rank drift.
Patrick Traill: Would anyone care to add information on how national amateur bodies deal with drift?
Rank inflation arguably occurs when there is a market for rank certificates, rank awards for achievements or self ranking without opportunities for demotion. Rank deflation is common in systems where rank is tied to rating when a growing or improving player population competes for a limited amount of rating points.
The impact of rank inflation may be exaggerated by rating enthusiasts, who would like to tie ranks strictly to ratings. There is, however, little evidence that these systems produce ranks better suited to determining appropriate handicaps or even games.