Design and setting
A population-based matched cohort
study was designed to estimate the effect of HRT on the hazards of
all-cause mortality using The Health Improvement Network (THIN)
database. The database holds retrospectively collected information of
anonymized patients from UK primary care dating back from the 1960s.
THIN is representative of the UK general population in terms of
demographics, prevalence of major medical conditions, and mortality
rates when adjusted for demographics and
deprivation.25 Currently, THIN database retains
longitudinal records of 17 million patients from over 770 GP practices,
of which 3.1 million are actively registered, covering 6.2% of the UK
population.26, 27