Table 2 Characteristics of the three cohort studies included in the trajectory modelling
Study name | Avon Longitudinal Study of Parents and Children (ALSPAC) | Bone Mineral Density in Childhood Study (BMDCS) | Pediatric Bone Mineral Accrual Study (PBMAS) |
|---|---|---|---|
Design | birth cohort study (started in 1990–1992) | child cohort study (started in 2002–2003) | child cohort study (started in 1991) |
Region and country | catchment area of 3 health authorities in Southwest England, UK | 5 USA clinic centres: Los Angeles, New York, Cincinnati, Omaha, Philadelphia | 2 elementary schools, Saskatoon, Saskatchewan, Canada |
Birth years | 1990–1992 | 1985–1997 | 1983–1976 |
Ethnicity | 98% white ethnicity | ethnically diverse | 95% white ethnicity |
DXA device used to measure BMC | Lunar Prodigy | Hologic QDR-4500A | Hologic QDR-2000 |
Mean age at the baseline/youngest DXA scan (range) | 9.9 years (8.8–11.7 years) | 10.8 years (6.0–17.0 years) | 11.8 years (8.0–15.1 years) |
Mean age at last/oldest DXA scan (range) | 24.6 years (22.4–26.5 years) | 16.1 years (6.9–23.3 years) | 37.3 years (34.3–40.2 years) |
Frequency and the maximum number of repeated DXA scans | up to 6 repeated scans at mean ages 9.9, 11.7, 13.8, 15.4, 17.8, and 24.6 years | up to 7 yearly repeated scans | Up to 16 repeated scans (1991–1998, 2003–2005, 2007–2011 and 2016–2017) |
Individuals included in the analysisa | 4007 females 3888 males | 488 females 465 males | 127 females 112 males |