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SciPy Reference Guide, Release 0.8.dev<br />

• (3/8,3/8): p(k) = (k-3/8)/(n+1/4). Blom. The resulting quantile estimates are approximately<br />

unbiased if x is normally distributed (R type 9)<br />

• (.4,.4) : approximately quantile unbiased (Cunnane)<br />

• (.35,.35): APL, used with PWM<br />

Parameters<br />

x : sequence<br />

pointbiserialr(x, y)<br />

Input data, as a sequence or array of dimension at most 2.<br />

prob<br />

[sequence] List of quantiles to compute.<br />

alpha<br />

[{0.4, float} optional] Plotting positions parameter.<br />

beta<br />

[{0.4, float} optional] Plotting positions parameter.<br />

Calculates a point biserial correlation coefficient and the associated<br />

p-value.<br />

Notes<br />

The point biserial correlation is used to measure the relationship between a binary variable, x, and a<br />

continuous variable, y. Like other correlation coefficients, this one varies between -1 and +1 with 0<br />

implying no correlation. Correlations of -1 or +1 imply a determinative relationship.<br />

Parameters<br />

x : array of bools<br />

y : array of floats<br />

Returns<br />

(point-biserial r, :<br />

2-tailed p-value)<br />

Missing values are considered pair-wise: if a value is missing in x, the corresponding value in y is masked.<br />

rankdata(data, axis=None, use_missing=False)<br />

Returns the rank (also known as order statistics) of each data point along the given axis.<br />

If some values are tied, their rank is averaged. If some values are masked, their rank is set to 0 if use_missing is<br />

False, or set to the average rank of the unmasked values if use_missing is True.<br />

Parameters<br />

data : sequence<br />

Input data. The data is transformed to a masked array<br />

axis<br />

[{None,int} optional] Axis along which to perform the ranking. If None, the<br />

array is first flattened. An exception is raised if the axis is specified for arrays<br />

with a dimension larger than 2<br />

3.18. Statistical functions (<strong>scipy</strong>.stats) 683

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