Welch's t-test: Difference between revisions

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This shows how pvalue can be calculated from any two arrays, using Welch's 2-sided t-test, which doesn't assume equal variance.

The high "n" value ensures roughly 6 digits convergence with Simpson's integral approximation.

<lang C>#include <stdio.h>

~~<lang C>~~double calculate_Pvalue (const double *array1, const size_t array1_size, const double *array2, const size_t array2_size) {

#include <math.h>

double calculate_Pvalue (const double *array1, const size_t array1_size, const double *array2, const size_t array2_size) {

if (array1_size <= 1) {

return 1.0;

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Line 101:

return return_value;

}

//-------------------

int main(void) {

const double d1[] = {27.5,21.0,19.0,23.6,17.0,17.9,16.9,20.1,21.9,22.6,23.1,19.6,19.0,21.7,21.4};

const double d2[] = {27.1,22.0,20.8,23.4,23.4,23.5,25.8,22.0,24.8,20.2,21.9,22.1,22.9,20.5,24.4};

const double d3[] = {17.2,20.9,22.6,18.1,21.7,21.4,23.5,24.2,14.7,21.8};

const double d4[] = {21.5,22.8,21.0,23.0,21.6,23.6,22.5,20.7,23.4,21.8,20.7,21.7,21.5,22.5,23.6,21.5,22.5,23.5,21.5,21.8};

const double d5[] = {19.8,20.4,19.6,17.8,18.5,18.9,18.3,18.9,19.5,22.0};

const double d6[] = {28.2,26.6,20.1,23.3,25.2,22.1,17.7,27.6,20.6,13.7,23.2,17.5,20.6,18.0,23.9,21.6,24.3,20.4,24.0,13.2};

const double d7[] = {30.02,29.99,30.11,29.97,30.01,29.99};

const double d8[] = {29.89,29.93,29.72,29.98,30.02,29.98};

const double x[] = {3.0,4.0,1.0,2.1};

const double y[] = {490.2,340.0,433.9};

printf("Test sets 1 p-value = %lf\n",calculate_Pvalue(d1,sizeof(d1)/sizeof(*d1),d2,sizeof(d2)/sizeof(*d2)));

printf("Test sets 2 p-value = %lf\n",calculate_Pvalue(d3,sizeof(d3)/sizeof(*d3),d4,sizeof(d4)/sizeof(*d4)));

printf("Test sets 3 p-value = %lf\n",calculate_Pvalue(d5,sizeof(d5)/sizeof(*d5),d6,sizeof(d6)/sizeof(*d6)));

printf("Test sets 4 p-value = %lf\n",calculate_Pvalue(d7,sizeof(d7)/sizeof(*d7),d8,sizeof(d8)/sizeof(*d8)));

printf("Test sets 5 p-value = %lf\n",calculate_Pvalue(x,sizeof(x)/sizeof(*x),y,sizeof(y)/sizeof(*y)));

return 0;

}

</lang>