#include "k.h"
/* 
*	Perform a chi-sq test using Armitage's additive model         
*	Input o (case) and e (control) (each vectors, length 3), R and N       
*	Output chi-sq value
*/
double chi(int *o, int *e, int R, int N) {
	
int n1,n2,r1,r2;
double num,den;

n1=o[1]+e[1];
n2=o[2]+e[2];
r1=o[1];
r2=o[2];
num=N*pow(N*(r1+2.*r2)-R*(n1+2.*n2),2.);			
den=R*(N-R)*(N*(n1+4.*n2)-pow(n1+2.*n2,2.));
return(sqrt(num/den));
}