def test_madmedianrule(self):
"""Test function madmedianrule."""
a = [1.2, 3, 4.5, 2.4, 5, 12.7, 0.4]
assert np.alltrue(
madmedianrule(a) ==
[False, False, False, False, False, True, False])
def skipped(x, y, method='spearman'):
"""
Skipped correlation (Rousselet and Pernet 2012).
Parameters
----------
x, y : array_like
First and second set of observations. x and y must be independent.
method : str
Method used to compute the correlation after outlier removal. Can be
either 'spearman' (default) or 'pearson'.
Returns
-------
r : float
Skipped correlation coefficient.
pval : float
Two-tailed p-value.
outliers : array of bool
Indicate if value is an outlier or not
Notes
-----
The skipped correlation involves multivariate outlier detection using a
projection technique (Wilcox, 2004, 2005). First, a robust estimator of
multivariate location and scatter, for instance the minimum covariance
determinant estimator (MCD; Rousseeuw, 1984; Rousseeuw and van Driessen,
1999; Hubert et al., 2008) is computed. Second, data points are
orthogonally projected on lines joining each of the data point to the
location estimator. Third, outliers are detected using a robust technique.
Finally, Spearman correlations are computed on the remaining data points
and calculations are adjusted by taking into account the dependency among
the remaining data points.
Code inspired by Matlab code from Cyril Pernet and Guillaume
Rousselet [1]_.
Requires scikit-learn.
References
----------
.. [1] Pernet CR, Wilcox R, Rousselet GA. Robust Correlation Analyses:
False Positive and Power Validation Using a New Open Source Matlab
Toolbox. Frontiers in Psychology. 2012;3:606.
doi:10.3389/fpsyg.2012.00606.
"""
# Check that sklearn is installed
from pingouin.utils import is_sklearn_installed
is_sklearn_installed(raise_error=True)
from scipy.stats import chi2
from sklearn.covariance import MinCovDet
X = np.column_stack((x, y))
center = MinCovDet().fit(X).location_
# Detect outliers based on robust covariance
nrows, ncols = X.shape
gval = np.sqrt(chi2.ppf(0.975, 2))
# Loop over rows
record = np.zeros(shape=(nrows, nrows))
for i in np.arange(nrows):
dis = np.zeros(nrows)
B = (X[i, :] - center).T
bot = np.sum(B**2)
if bot != 0:
for j in np.arange(nrows):
A = X[j, :] - center
dis[j] = np.linalg.norm(A * B / bot * B)
# Apply the MAD median rule
MAD = mad(dis)
outliers = madmedianrule(dis)
record[i, :] = dis > (np.median(dis) + gval * MAD)
outliers = np.sum(record, axis=0) >= 1
# Compute correlation on remaining data
if method == 'spearman':
r, pval = spearmanr(X[~outliers, 0], X[~outliers, 1])
else:
r, pval = pearsonr(X[~outliers, 0], X[~outliers, 1])
return r, pval, outliers
