Best Practices for Energy Price Indices © Copyright 2003, CCRO. All rights reserved. 13 should be clear, consistently applied to all data providers, and completed in a timely manner. The index developer may choose to define a materiality threshold for error revisions to limit resubmission to significant errors only and may define a materiality threshold for index changes. The designated noncommercial group should initiate in writing any error revision requests. 4.1.11 Establish a Challenge Process – After Index Publication A challenge process should apply when submitted data is suspected of having been excluded from the index calculation or when other serious grounds exist for questioning an index value that has already been published. The index developer, in consultation with data providers, should determine a priori materiality thresholds for the challenge process as an integral part of the index methodology. An index challenge may be initiated in writing from any index user and, for a data provider, should originate only from the designated noncommercial group. The actual mechanics for ensuring a speedy error correction and challenge process while preventing frivolous and time-consuming or overly outdated challenges can be addressed by the index developer and the data providers in the respective protocols or in the documentation regarding the index methodology. 4.1.12 Index Revision Process If error revisions or challenges received exceed certain materiality thresholds determined and published by the index developer,2 the index developer should reexamine the index calculation and the data sets to ensure that material errors are corrected. If the published index is still materially correct, the index developer should notify all challenging data providers in a timely manner otherwise, the developer should revise the index value. The index developer should set explicit deadlines until which resubmissions under the error revision process and challenges under the challenge process will be accepted. The deadlines should be based on the demands of the index and be set in consultation with the data providers and index users. Exhibit A provides an illustrative timeline. 4.1.13 Information Accompanying Published Index Value In addition to the index value, the index developers should, for liquid and illiquid markets, publish other aggregate information such as the common price range, total transaction volume(s) used to calculate the index, and descriptive statistics such as histograms or box-and-whisker plots. This would serve to indicate how robust and reliable an index is and enhance market transparency. 4.1.14 Documenting Index Construction Methodology Each index developer should publish the methodology used for deriving a given index, including the methodology used in case of insufficient data and the processes and materiality thresholds used for error revisions and challenges. 2 What is material in the data set of an individual data provider may not be material relative to all data sets received by the index provider. Hence, yet another set of materiality thresholds may apply.