Additional reference GFR measurements will be undertaken after 1 and 2 years to enable a model of disease progression and error to be built .3 ) A biological variability study to establish reference change values for reference and test measures .4 ) A modelling study of the performance of monitoring strategies on detecting progression , utilising estimates of accuracy , patterns of disease progression and estimates of measurement error from studies 1 ) , 2 ) and 3 ) .5 ) A comprehensive cost database for each diagnostic approach will be developed to enable cost-effectiveness modelling of the optimal strategy.The performance of the estimating equations will be evaluated by assessing bias , precision and accuracy .