〔例2-17〕在一项某中药治疗感染性腹泻的III 临床试验中，设计安排3 种干预，即高剂量药物组、低剂量药物组和安慰剂组，主要疗效指标为愈显率。根据

II 期临床试验数据，3个组的愈显率分别为60%、50%和40%，试以平衡设计、双侧检验水准0. 05、检验效能90%估计最低样本量。

SAS9. 2 软件实现:

%macro PGT0( p，v，alpha，g，power) ;

data PGT0;

g = ＆g;

p1 = 0. 6;

p2 = 0. 5;

p3 = 0. 4;

alpha = ＆alpha;

power = ＆power;

if ＆p = . then p = ( p1+ p2 + p3) /3;

else p = ＆p;

if ＆v = . then v = ( (p1-p) ＊＊2 + ( p2-p) ＊＊2 + ( p3-p) ＊＊2) /g;

else v = ＆v;

h = v /( p* ( 1-p) ) ;

n = 0;

do until( abs( p1-power) ＜ = 0. 001) ;

p1 = 1-cdf ( 'CHISQUARE'，cinv (1-alpha，g-1) ，g-1，g * n* h) ;

end;

n = n + 1;

p1 = 0. 6;

run;

proc print data = PGT0 label;

var alpha p1 p2 p3 g power n;

label alpha = 'Test significance level'

p1 = 'proportion1'

p2 = 'proportion2'

p3 = 'proportion3'

power = 'Power'

n = 'n';

quit;

%mend PGT0;

%PGT0( p = . ，v = . ，alpha = 0. 05，g = 3，power =0. 90) ;