WD = Withdrawn, DOB = date of birth, yrs = years.
1–3 Figure 1 outlines the follow-up over the past five decades, which is described in detail in the sections below.įollow-up and response rates of the TAHS probands from 1968 to 2012. Details of these follow-ups have been described previously. The TAHS is a population-based prospective cohort study, which has been followed up from 1968 until the current follow-up when participants are in their sixth decade of life. Who is in the cohort, how often have they been followed up, and what is attrition like? The original study investigators planned to recruit another cohort of 7-year-old children in 4 years from the 1968 study, to investigate secular trends in asthma incidence, but this was never undertaken. Since the baseline survey, the cohort has been followed up several times as outlined below. At the baseline survey, questionnaires on both parents and all siblings were also collected, making the TAHS one of the first and largest family studies of respiratory disease in the world. This was: (i) to ensure that participants were old enough to adequately perform spirometry manoeuvres (ii) to ensure that participants were young enough to allow for follow-up of at least 7 years through the school system and (iii) to reduce parental recall error of early life exposures and symptoms by limiting the recall time to a maximum of 7 years. The original study cohort consisted of all Tasmanian school children born in 1961, who would be aged 7 years at the time of the baseline survey. The original aims of the survey were to provide an epidemiological description of childhood asthma, which has a variable natural history requiring: (i) an estimate of its prevalence among children of a suitable age (ii) an estimate of the probability that an individual will change disease status during any given period and (iii) an estimate of any secular trend, specifically any tendency for the incidence to vary over time.
1 In 1967 the Tasmanian Health Minister, who was the head of the School Health Service, gave his approval to carry out the survey on all children born in 1961 and attending school in the island state of Tasmania, Australia. The Tasmanian Longitudinal Health Study (TAHS), originally named the Tasmanian Asthma Survey, was initiated to examine the prevalence and natural history of asthma in childhood.
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