Chauvenet's criterion

gistfile1.txt

# In statistical theory, Chauvenet's criterion (named for William Chauvenet[1]) is a means of assessing whether 
# one piece of experimental data — an outlier — from a set of observations, is likely to be spurious.
# https://en.wikipedia.org/wiki/Chauvenet%27s_criterion

def chauvenet(array):
    mean = array.mean()           # Mean of incoming array
    stdv = array.std()            # Standard deviation
    N = len(array)                # Lenght of incoming array
    criterion = 1.0/(2*N)         # Chauvenet's criterion
    d = abs(array-mean)/stdv      # Distance of a value to mean in stdv's
    prob = erfc(d)                # Area normal dist.    
    return prob < criterion       # Use boolean array outside this function