class_docstr: Results class for OrderedModel
  
  This class inherits from GenericLikelihoodModelResults and not all
  inherited methods might be appropriate in this case.
docstr: McFadden's pseudo-R-squared. `1 - (llf / llnull)`
code: def prsquared(self):
      """
      McFadden's pseudo-R-squared. `1 - (llf / llnull)`
      """
      return 1 - self.llf / self.llnull
  
imports: import warnings
  from statsmodels.compat.pandas import Appender
  import numpy
  import pandas
  from pandas.api.types import CategoricalDtype
  from scipy import stats
  from statsmodels.base.model import Model, LikelihoodModel, GenericLikelihoodModel, GenericLikelihoodModelResults
  import statsmodels.base.wrapper
  import statsmodels.regression.linear_model
  from statsmodels.tools.decorators import cache_readonly
label_desc: Use image node_id 3 for calling the OrderedResults obj's underlying member method code with example usage: obj.prsquared() and returns: unknown