code: def _create_latent_variables(self):
          
  
          self.latent_variables.add_z('Constant', fam.Normal(0,10,transform=None), fam.Normal(0,3))
          self.latent_variables.add_z('Ability Scale', fam.Normal(0,1,transform=None), fam.Normal(0,3))
docs: Creates model latent variables
  
          Returns
          ----------
          None (changes model attributes)