code: def _ci(
      arr,
      ci=0.95,
      method="bootstrap",
      n_bootstraps=2000,
      random_state=None,
  ):
      """Calculate confidence interval. Aux function for plot_compare_evokeds."""
      if method == "bootstrap":
          return bootstrap_confidence_interval(
              arr,
              ci=ci,
              n_bootstraps=n_bootstraps,
              random_state=random_state,
          )
      else:
          from .parametric import _parametric_ci
  
          return _parametric_ci(arr, ci=ci)
  
imports: from math import sqrt
  import numpy
  from ..parallel import parallel_func
  from ..utils import check_random_state, logger, verbose
label_desc: Use image node_id 4 for calling a global function with example usage: _ci(arr, ci, method, n_bootstraps, random_state) and returns: bootstrap_confidence_interval, _parametric_ci