The EXPAND procedure provides time interval conversion and missing value interpolation for time series.
The features of the EXPAND procedure include
conversion of time series frequency; for example, constructing quarterly estimates from annual series or aggregating quarterly values to annual
conversion of irregular observations to periodic estimates
interpolation of missing values in time series
conversion of observation types; for example, estimate stocks from flows and vice versa. All possible conversions supported between
beginning-of-period
end-of-period
period midpoint
period total
period average
conversion of time series phase shift; for example, conversion between fiscal years and calendar years
choice of four interpolation methods: cubic splines, linear splines, step functions, and simple aggregation
PROC EXPAND enables you to control the end point constraints used to fit interpolating cubic spline curves. In addition, you can transform series before and after interpolation (or without interpolation) using any combination of the following:
shift by constant square root lags scale by constant square leads change sign logistic differences absolute value inverse logistic cumulative sum reciprocate upper bounds moving sum logarithm lower bounds moving average exponential reverse seriesThe EXPAND procedure offers support for a wide range of time series frequencies:
YEAR SEMIMONTH DAY SEMIYEAR TENDAY HOUR QUARTER WEEK MINUTE MONTH WEEKDAY SECOND
The basic interval types can be repeated or shifted to define a great variety of different frequencies, such as fiscal years, biennial periods, work shifts, and so forth.
For further details, see the SAS/ETS^{®} User's Guide