DM 'LOG;CLEAR;OUT;CLEAR';
OPTIONS NODATE NONUMBER LS=76 PS=54;

DATA trees;
 INPUT photo field @@;
   N = 100;
DATALINES;
10 15   12 14    7  9   13 14   13  8    6  5   17 18
16 15   15 13   10 15   14 11   12 15   10 12    5  8
12 13   10  9   10 11    9 12    6  9   11 12    7 13
 9 11   11 10   10  9   10  8
;

/* Use proc surveyreg to estimate the total number of trees */

PROC SURVEYREG DATA=trees TOTAL=100;
     MODEL field = photo / clparm solution df=23;
     ESTIMATE 'Total field trees' intercept 100 photo 1130;

/* substitute N for intercept, t_x for photo */
   ESTIMATE 'Mean field trees' intercept 100 photo 1130 / divisor=100;
run;