stats.py 文件源码

def achisquare(f_obs,f_exp=None):
    """
    Calculates a one-way chi square for array of observed frequencies and returns
    the result.  If no expected frequencies are given, the total N is assumed to
    be equally distributed across all groups (NOT RIGHT??)

    Usage:   achisquare(f_obs, f_exp=None)   f_obs = array of observed cell freq.
    Returns: chisquare-statistic, associated p-value
    """

    k = len(f_obs)
    if f_exp == None:
        f_exp = N.array([sum(f_obs)/float(k)] * len(f_obs),N.float_)
    f_exp = f_exp.astype(N.float_)
    chisq = N.add.reduce((f_obs-f_exp)**2 / f_exp)
    return chisq, achisqprob(chisq, k-1)