Note that the data must be sorted by sample date.
A. Initial analysis for examining the ACF and PACF ratios.
PROC ARIMA; /* compute the ACF and PACF */
IDENTIFY VAR=LOGREF; /* ACF and PACF plots produced automatically */
B. Based on the initial analysis, a model of order p = 1 is fit to the data.
PROC ARIMA; /* fit an AR(1) model */
ESTIMATE P=1 /* P = order of model */
MAXIT=30 /* maximum number of iterations = 30 */
METHOD=ML /* use maximum likelihood */
PLOT; /* plot ACF and PACF residuals to test for model fit */
/*** Similar analyses of reference and treatment basins not shown for brevity ***/