code: def _zscore(x):
      # helper function
      return (x - x.mean(0)) / x.std(0)
  
file_path: statsmodels/statsmodels/multivariate/tests/test_factor.py
imports: import warnings
  from statsmodels.compat.pandas import PD_LT_1_4
  import os
  import numpy
  import pandas
  from statsmodels.multivariate.factor import Factor
  from numpy.testing import assert_equal, assert_array_almost_equal, assert_, assert_raises, assert_array_equal, assert_array_less, assert_allclose
  import pytest
label_desc: Use image node_id 8 for calling a global function with example usage: _zscore(x) and returns: unknown