by regulation for the purposes of, and only to the extent necessary in, the structuring of censuses and national economic accounts and conducting related statistical activities authorized by law. (11) Department of the treasury Returns and return information shall be open for inspection by officers and employees of the Department of the Treasury whose official duties require such inspection or disclosure for the purpose of, and only to the extent necessary for, preparing economic or financial forecasts, projections, analyses, or estimates. Such inspection or disclosure shall be permitted only upon written request that sets forth the reasons why such inspection or disclosure is necessary and is signed by the head of the bureau or office of the Department of the Treasury requesting the inspection or disclosure. 606. Installment agreements