Statistical methodology for age-adjustment of the GH-2000 score detecting growth hormone misuseReport as inadecuate

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BMC Medical Research Methodology

, 16:147

Data analysis, statistics and modelling


BackgroundThe 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.

MethodsWe 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.

ResultsThe 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.

ConclusionsA final revised GH-2000 score formula is provided which is independent of the age of the athlete under consideration.

KeywordsGH-2000 score Adjusting for age effects Meta-analysis of scores Centring and norming of scores AbbreviationsGH-2000 scoreGrowth hormone 2000 score

DLDecision limit

IGF-IInsulin-like growth factor-I

P-III-NPAmino-terminal pro-peptide of type III collagen

LC-MS-MSImmunotech, IDS are assays to measure IGF-I

Siemens-CentaurOrion are assays to measure P-III-NP

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Author: Dankmar Böhning - Walailuck Böhning - Nishan Guha - David A. Cowan - Peter H. Sönksen - Richard I. G. Holt



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