Interaction Checker - How are Minor, Moderate, Major determined?

From a drug interactions results page: e.g.
https://www.drugs.com/drug-interactions/atorvastatin,lipitor.html

Drug Interaction Classification
These classifications are only a guideline. The relevance of a particular drug interaction to a specific individual is difficult to determine. Always consult your health care provider before starting or stopping any medication.

Major: Highly clinically significant. Avoid combinations; the risk of the interaction outweighs the benefit.

Moderate: Moderately clinically significant. Usually avoid combinations; use it only under special circumstances.

Minor: Minimally clinically significant. Minimize risk; assess risk and consider an alternative drug, take steps to circumvent the interaction risk and/or institute a monitoring plan.