diff --git a/tableone/modality.py b/tableone/modality.py
index bc28f15..4b8c7a4 100644
--- a/tableone/modality.py
+++ b/tableone/modality.py
@@ -1074,7 +1074,7 @@ def least_concave_majorant_sorted(x, y, eps=1e-12):
     return np.array(i)
 
 
-class KernelDensityDerivative(object):
+class KernelDensityDerivative:
     """
     Kernel density derivative estimator.
 
@@ -1302,7 +1302,7 @@ def gamma(beta): return 2*beta*betafun(beta-1./2, 1./2)**2 - d_hat
     return RefStudentt(beta)
 
 
-class RefGaussian(object):
+class RefGaussian:
     """
     Reference Gaussian distribution for generating random samples.
 
@@ -1322,7 +1322,7 @@ def sample(self, n):
         return np.random.randn(n)
 
 
-class RefBeta(object):
+class RefBeta:
     """
     Reference Beta distribution for generating random samples, parameterized by a shape parameter.
 
@@ -1348,7 +1348,7 @@ def sample(self, n):
         return np.random.beta(self.beta, self.beta, n)
 
 
-class RefStudentt(object):
+class RefStudentt:
     """
     Reference Student's t distribution for generating random samples, parameterized by a degrees of freedom parameter.