title: Statistical methodology for age-adjustment of the GH-2000 score detecting growth hormone misuse.
abstract: The GH-2000 score has been developed as a powerful and unique technique for the detection of growth hormone misuse by sportsmen and women. The score depends upon the measurement of two growth hormone (GH) sensitive markers, insulin-like growth factor-I (IGF-I) and the amino-terminal pro-peptide of type III collagen (P-III-NP). With the collection and establishment of an increasingly large database it has become apparent that the score shows a positive age effect in the male athlete population, which could potentially place older male athletes at a disadvantage.
  
  
  
  We have used results from residual analysis of the general linear model to show that the residual of the GH-2000 score when regressed on the mean-age centred age is an appropriate way to proceed to correct this bias. As six GH-2000 scores are possible depending on the assays used for determining IGF-I and P-III-NP, methodology had to be explored for including six different age effects into a unique residual. Meta-analytic techniques have been utilized to find a summary age effect.
  
  
  
  The age-adjusted GH-2000 score, a form of residual, has similar mean and variance as the original GH-2000 score and, hence, the developed decision limits show negligible change when compared to the decision limits based on the original score. We also show that any further scale-transformation will not change the adjusted score. Hence the suggested adjustment is optimal for the given data. The summary age effect is homogeneous across the six scores, and so the generic adjustment of the GH-2000 score formula is justified.
  
  
  
  A final revised GH-2000 score formula is provided which is independent of the age of the athlete under consideration.
authors: Southampton Statistical Sciences Research Institute, University of Southampton, Southampton, SO17 1BJ, UK. d.a.bohning@soton.ac.uk.
authors: Dankmar
authors: 0000-0003-0638-7106
authors: D
authors: Böhning
authors: Human Development and Health Academic Unit, University of Southampton Faculty of Medicine, IDS Building (MP887), Southampton General Hospital, Tremona Road, Southampton, SO16 6YD, UK.
authors: Walailuck
authors: W
authors: Böhning
authors: Human Development and Health Academic Unit, University of Southampton Faculty of Medicine, IDS Building (MP887), Southampton General Hospital, Tremona Road, Southampton, SO16 6YD, UK.|Nuffield Division of Clinical Laboratory Sciences, UK Department of Clinical Biochemistry Level 4, University of Oxford, John Radcliffe Hospital Headley Way, Headington, Oxford, OX3 9DU, UK.
authors: Nishan
authors: N
authors: Guha
authors: Department of Pharmacy and Forensic Science, Drug Control Centre, King's College London, 150 Stamford Street, London, SE1 9NH, UK.
authors: David A
authors: DA
authors: Cowan
authors: Human Development and Health Academic Unit, University of Southampton Faculty of Medicine, IDS Building (MP887), Southampton General Hospital, Tremona Road, Southampton, SO16 6YD, UK.
authors: Peter H
authors: PH
authors: Sönksen
authors: Human Development and Health Academic Unit, University of Southampton Faculty of Medicine, IDS Building (MP887), Southampton General Hospital, Tremona Road, Southampton, SO16 6YD, UK.
authors: Richard I G
authors: RI
authors: Holt
mesh_terms: D000328:Adult; D000367:Age Factors; D000465:Algorithms; D045930:Anabolic Agents / Q000008:administration & dosage; D056352:Athletes; D001699:Biometry / Q000379:methods*; D004300:Doping in Sports / Q000517:prevention & control / Q000706:statistics & numerical data*; D005260:Female; D019382:Human Growth Hormone / Q000008:administration & dosage*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D016014:Linear Models; D008297:Male; D008962:Models, Theoretical; D010446:Peptide Fragments / Q000032:analysis; D011347:Procollagen / Q000032:analysis; D013177:Sports; D015813:Substance Abuse Detection / Q000379:methods*; D055815:Young Adult
chemical_list: D045930:Anabolic Agents; D010446:Peptide Fragments; D011347:Procollagen; C041876:procollagen Type III-N-terminal peptide; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I
keywords: Adjusting for age effects; Centring and norming of scores; GH-2000 score; Meta-analysis of scores