Explaining variation in referral from primary to secondary care: cohort study.

Objectives: To determine the extent to which referral for defined symptoms from primary care varies by age, sex, and social deprivation and whether any sociodemographic variations in referral differ according to the presence of national referral guidance and the potential of the symptoms to be life threatening.

Design: Cohort study using individual patient data from the health improvement network database in primary care.

Setting: United Kingdom.