Chi square test function. It returns if the null hypothesis can be discarded at significativity
level sig_level.
Parameters:
pearson_stat - value of the computed Pearson statistics
freedom_degree - degree of freedom for the chi square test.
sig_level - significativity level by which the null hypothesis can be discarded.
Returns:
1 if the null hyphotesis can be discarded at significativity level sig_level, 0 otherwise.