Concept drift in machine learning and data mining refers to the change in the relationships between input and output data in the underlying problem over time.
The change to the data could take any form. It is conceptually easier to consider the case where there is some temporal consistency to the change such that data collected within a specific time period show the same relationship and that this relationship changes smoothly over time.
Note that this is not always the case and this assumption should be challenged. Some other types of changes may include:
- A gradual change over time.
- A recurring or cyclical change.
- A sudden or abrupt change.
Different concept drift detection and handling schemes may be required for each situation. Often, recurring change and long-term trends are considered systematic and can be explicitly identified and handled.
Concept drift may be present on supervised learning problems where predictions are made and data is collected over time. These are traditionally called online learning problems, given the change expected in the data over time.
There are domains where predictions are ordered by time, such as time series forecasting and predictions on streaming data where the problem of concept drift is more likely and should be explicitly tested for and addressed.
A common challenge when mining data streams is that the data streams are not always strictly stationary, i.e., the concept of data (underlying distribution of incoming data) unpredictably drifts over time. This has encouraged the need to detect these concept drifts in the data streams in a timely manner
Indre Zliobaite in the 2010 paper titled “Learning under Concept Drift: An Overview” provides a framework for thinking about concept drift and the decisions required by the machine learning practitioner, as follows:
- Future assumption : a designer needs to make an assumption about the future data source.
- Change type : a designer needs to identify possible change patterns.
- Learner adaptivity : based on the change type and the future assumption, a designer chooses the mechanisms which make the learner adaptive.
- Model selection : a designer needs a criterion to choose a particular parametrization of the selected learner at every time step (e.g. the weights for ensemble members, the window size for variable window method).
This framework may help in thinking about the decision points available to you when addressing concept drift on your own predictive modeling problems.