; (III) the amount of unprocessed taxpayer correspondence, including tax returns, responses to Internal Revenue Service notices, tax payments, and other similar types of correspondence; and (IV) the median and average length of time for processing the items described in subclause (III) and processing refund claims. (iii) An analysis identifying any increase or decrease in total annual audits and annual audit rates by income group for the period beginning in 2018 and ending with the year the report is submitted. Such analysis shall include a detailed description of what constitutes an audit by the Internal Revenue Service, and if the definition of an audit used by the Internal Revenue Service differs from the definition used by the National Taxpayer Advocate, the Comptroller General of the United States, or the Treasury Inspector General for Tax Administration, there shall also be included an analysis using such divergent definition. (iv) A categorizing of the number of audits for each year in the analysis described in clause (iv) which were— (I) correspondence audits; (II) office audits; (III) field audits; (IV) audits under the Internal Revenue Service National Research Program