Sec. 4. For purposes of section 3 of this chapter, Indiana nonfarm personal income is the estimate of total nonfarm personal income for Indiana in a calendar year as computed by the federal Bureau of Economic Analysis before December 31 immediately preceding the beginning of the first state fiscal year in a biennial budget period, using any:
(1) actual data available for the calendar year; and
(2) estimated data for the calendar year whenever actual data is not available.