code: def check_statistics2(self, x, y):
      x = chainer.Variable(x)
      y = chainer.Variable(y)
      self.link(x, finetune=True)
      self.link(y, finetune=True)
      mean = (self.x.sum(axis=0) + self.y.sum(axis=0)) / (
          self.nx + self.ny
      )
      var = (
          self.x.var(axis=0) * self.nx + self.y.var(axis=0) * self.ny
      ) / (self.nx + self.ny)
  
      # TODO(Kenta Oono)
      # Fix the estimate of the unbiased variance.
      # Unbiased variance should be (nx + ny) / (nx + ny - 1) times of
      # the variance.
      # But the multiplier is ny / (ny - 1) in current implementation
      # these two values are different when nx is not equal to ny.
      unbiased_var = var * self.ny / (self.ny - 1)
      testing.assert_allclose(self.link.avg_mean, mean)
      testing.assert_allclose(self.link.avg_var, unbiased_var)
  
imports: import unittest
  import numpy
  import six
  import chainer
  from chainer.backends import cuda
  from chainer import links
  from chainer import testing
  from chainer.testing import attr
label_desc: Use image node_id 5 for calling the TestPopulationStatistics obj's underlying member method code with example usage: obj.check_statistics2(x, y) without return types