Table A-1. SEASONAL INDEXES USED TO ADJUST PRIVATE HOUSING STARTS: MONTHLY 1976 TO 1977

'The implicit seasonal index is the ratio of the unadjusted number of housing units started in the United States to the seasonally adjusted national totals of housing units started.

Table A-2. SEASONAL INDEXES TO ADJUST HOUSING UNITS AUTHORIZED IN PERMIT-ISSUING PLACES AND MANUFACTURERS' SHIPMENTS OF MOBILE HOMES: MONTHLY 1976 TO 1977

The implicit seasonal index is the ratio of the unadjusted number of housing units authorized by building permits in the United States to the seasonally adjusted national totals of housing units authorized. The implicit index does not include mobile home shipments.

Table A-3. AVERAGE PERCENTAGE CHANGES AND RELATED MEASURES FOR MONTHLY HOUSING STARTS, PERMIT AUTHORIZATIONS, AND MOBILE HOME SHIPMENTS

The following are brief definitions of the measures shown in this table. More complete explanations appear in Electronic Computers and Business Indicators by Julius Shiskin, issued as Occasional Paper 57 by the National Bureau of Economic Research, 1957 (reprinted from the Journal of Business, October 1957).

'O' is the average month-to-month percentage change, without regard to sign, in the original series.

'CI' is the average month-to-month percentage change, without regard to sign, in the seasonally adjusted series.

'I' is the average month-to-month percentage change, without regard to sign, for the irregular component, which is obtained by dividing the cyclical component into the seasonally adjusted series.

'C' is the average month-to-month percentage change, without regard to sign, in the cyclical component. 'C' is a smooth, flexible moving average of the seasonally adjusted series.

'I/C' is the average month-to-month percentage change, without regard to sign, of the irregular component divided by the average month-tomonth percentage change, without regard to sign, of the cyclical component. It serves as an indication of the series' relative smoothness (small values) or irregularity (large values).

MCD (months for cyclical dominance) gives an estimate of the appropriate time span over which to observe cyclical movement in a monthly series. In deriving MCD the average (without regard to sign) percentage changes in the irregular and in the cyclical component are computed for 1-month spans (Jan.-Feb., Feb.-Mar., etc.), 2-month spans (Jan.-Mar., Feb. -Apr., etc.) up to 5-month spans. MCD is the shortest span for which the average change (without regard to sign) in the cyclical component is larger than the average change (without regard to sign) in the irregular component; thus it indicates the point at which fluctuations begin to be more attributable to cyclical than to irregular movements. Since changes are not computed for spans greater than 5 months, all series with an MCD greater than "5" are shown as "6". MCD is small for smooth series and large for erratic series.