May the parties access the data underlying expert or opinion testimony? The presiding officer or other appropriate officer, in her/his discretion but consistent with the rights of the parties, may cause the parties to make available for inspection in advance of the hearing, and for purposes of cross-examination at the hearing, the data underlying expert or opinion testimony including testimony based on economic and statistical data. Wherever practicable, she/he will restrict to a minimum the placing of such data in the record.