Journal of Biometrics & Biostatistics

Paula L Hedley

Publications

• Research Article
  The Concepts of Fractal Ellipses and ISO Likelihood Ratio Curve s in Two-dimensional Screening Procedures with Applications in Scree ning for Down Syndrome
  Author(s): Severin Olesen Larsen, Paula L Hedley and Michael ChristiansenSeverin Olesen Larsen, Paula L Hedley and Michael Christiansen
  
  Background: Prenatal screening combines biochemical and biometric markers into a risk estimate for a particular adverse outcome, e.g. the birth of a child with Down syndrome. The statistical calculations are complicated. We describe a simple graphical method to perform risk estimation in the case of two biochemical markers, to assess the consequences of changes in gestational dating of the pregnancy and to perform quality control. Materials and methods: We used the formulae for the Normal distribution to establish the expression for fractal ellipses, i.e. contour ellipses describing a certain fractile of the total distribution. This expression was used to establish mathematical expressions for curves describing two-dimensional pairs of analytes giving the same likelihood-ratio, i.e. iso likelihood-ratio curves. Results: The fractal ellipses provide an over.. Read More»
  DOI: 10.4172/2155-6180.1000255

  Abstract PDF