Enrolment was coded as '1' if the respondent did enrol in the scheme; and '0' if the respondent did not.
Upon enrolment, alphanumeric identification codes were assigned to the patients who were then randomised to one of the two treatments.
Mortality was identified from a combination of READ codes, registration status, additional health data codes and enrolment dates.
Mean county-level residential radon concentrations were linked to study participants' residential address based on their ZIP code at enrolment (mean± sd 53.5±38.0 Bq·m−3).
All participating children will be given an enrolment number (including a code for school), which will be recorded on the final list of eligible children, printed on all enquiry tools and entered in the database.
The use of different coders (who have no previous knowledge of patient enrolment and randomization to code separately for infant facial responses, etc and who will remain blinded to each other's assessments), is expected to minimize observer bias.
Written consent will be taken from each participant on enrolment and a unique identifier code will protect each participant's anonymity alongside published verbatim quotes taken from the transcripts.
Demographic, clinical, laboratory and dialysis-related data were obtained from a centralised database within 1 month of enrolment using a standardised identification code to link study procedures to database information.
Study participants were assigned to a primary county of residence using five-digit ZIP code information provided at enrolment, according to the ZIP code boundaries of the 1980 US Census [ 18].
The randomisation code remained secured until enrolment and data entry were complete.
