data g; input X	Y;
cow= _n_;
datalines;
1	 1.8
1.5	 1.85
1.5	 1.87
1.5	 1.77
2.5	 2.02
4	 2.27
5	 2.15
5	 2.26
7	 2.47
8	 2.19
8.5	 2.26
9	 2.4
9.5	 2.39
9.5	 2.41
10	 2.5
12	 2.32
12	 2.32
13	 2.43
13   2.47
14.5 2.56
15.5 2.65
15.5 2.47
16.5 2.64
17   2.56
22.5 2.7
29	 2.72
31.5 2.57
;
run;
proc gplot data=g;
  plot y*x;
run;
proc nlin data=g;
  parms alpha 1 beta 1 gamma 0.5;
  bounds 0 < gamma <1;
  model y = alpha - beta*gamma**x;
  der.alpha=1;
  der.beta=-gamma**x;
  der.gamma=-x*beta*gamma**(x-1);
  output out=ap predicted=yhat l95m=lb u95m=ub;
run;