Disenrollment from a health insurance plan expressed as a percentage of total membership. For example, a managed care plan with 40,000 members with a 2% attrition rate would need to gain 800 new members each month to retain the initial 40,000 covered lives.
Insurance Encyclopedia
Attritional loss ratio
The measure of residual insurance claims as a percentage of earned premiums (net of reinsurance). Attritional insurance claims are calculated as total claims with major losses and movements in prior year claims reserves subtracted.