The policy year experience for an individual insurance policy includes each premium and loss transaction that relates to that particular policy. An aggregate policy year experience for an entire book of business is calculated by including the individual experience of all policies that became effective during that year. For example, 20YY policy year data would include the experience of all policies effective between January 1, 20YY, and December 31, 20YY, regardless of the date on which losses or other events associated with those policies occur. This approach provides a clear match between losses and premiums.