These investigators examined the association between death of a child and parental admission to a mental hospital. All information was obtained from a national database with records for over 1 million people in Denmark who had at least one child under the age of 18 at some point during the follow-up period from 1970-1999. Parents who lost a child during this period were categorized as "bereaved". Parents whose children did not die during the study period were "non-bereaved."

ALL SUBJECTS	Hospital Admissions	Person-Years
Bereaved	527	175,281
Non-bereaved	20,186	11,436,168

Calculate the incidence rate ratio for the relationship between being bereaved, compared to non-bereaved, and parental admission to a mental hospital in Denmark from 1970-1999.