Inclusions and exclusions
Participants were eligible for the study if at the time of study entry,
they had been registered as an active patient for at least one year, and
their health records had been accessed at least once within the past ten
years from their study entry date.
To avoid bias due to ‘immortal
periods’, actively registered patients who were prescribed HRT after the
acceptable mortality reporting (AMR) date (a starting date from which
practice recorded mortality was close to age- and sex-standardized
national mortality rates) of the corresponding GP practice were selected
for the study. Patients with a previous history of any kind of cancer,
acute myocardial infarction, serious heart failure, stroke (except
transient ischaemic attack), chronic kidney disease (stage 3 to 5),
dementia, premature ovarian insufficiency, surgically induced menopause
before 45, and premature menopause were excluded from the study at
baseline.
The analyses included patients who were born between 1921 and 1960 and
started HRT at the selected age from 1984 until the study end date which
was 1st January 2017, and their matched controls. Participants were
followed up from the date of first HRT prescription until death, or
transferred out, or study end date whichever comes first. Patients who
were transferred out during the study period were no longer followed up,
and their observation time was censored at that point of time. The SQL
server 2016 was used to extract data from THIN.