of statistical methods to characterise early growth and its impact on bone mineral content

61 Background Many statistical methods are available to model longitudinal growth data and 62 relate derived summary measures to later outcomes. 63 Aim To apply and compare commonly used methods to a realistic scenario including pre- and 64 postnatal data, missing data and confounders. 65 Subjects and methods Data were collected from 753 offspring in the Southampton Women’s 66 Survey with measurements of bone mineral content (BMC) at age 6 years. Ultrasound 67 measures included crown-rump length (11 weeks ’ gestation) and femur length (19 and 34 68 weeks ’ gestation); postnatally, infant length (birth, 6 and 12 months) and height (2 and 3 69 years) were measured. A residual growth model, two-stage multilevel linear spline model, 70 joint multilevel linear spline model, SITAR and a growth mixture model were used to relate 71 growth to 6-year BMC. 72 Results Results from the residual growth, two-stage and joint multilevel linear spline models 73 were most comparable: an increase in length at all ages was positively associated with BMC, 74 the strongest association being with later growth. Both SITAR and the growth mixture model 75 demonstrated that length was positively associated with BMC. 76 Conclusions Similarities and differences in results from a variety of analytic strategies need 77 to be understood in the context of each statistical methodology. 78