diff --git a/setup.py b/setup.py
index 995ef2f..cb023d8 100644
--- a/setup.py
+++ b/setup.py
@@ -28,7 +28,7 @@ def readme():
 
 setup(
     name='statscounter',
-    version='0.0.010',
+    version='0.0.011',
     url='https://github.com/datalib/statscounter',
     license='MIT',
     description="Python's missing statistical Swiss Army knife",
diff --git a/statscounter/statscounter.py b/statscounter/statscounter.py
index 2d4501c..3a2e16c 100644
--- a/statscounter/statscounter.py
+++ b/statscounter/statscounter.py
@@ -25,60 +25,104 @@
 import statscounter.stats as stats
 
 
+NUMBER_TYPES = set(['float', 'int', 'Decimal', 'Fraction'])
+
+
+class MultipleMostCommonValuesError(ValueError):
+	""""""
+	pass
+
+
 class StatsCounter(Counter):
+	
+	def key_types_distribution(self):
+		"""Return a p. distribution of the elements' types"""
+		return StatsCounter([type(element).__name__ 
+							 for element in self.elements()]).normalize()
+		
 	def mean(self):
+		""" AKA Expectation
+		"""
+		try:
+			return stats.mean(self.elements())
+		except (TypeError):
+			raise TypeError("Distribution is not a numerical type.")
+		
+	def expectation(self):
 		"""
 		"""
-		return stats.mean(self.values())
+		return self.mean()
 
 	def median(self, ):
 		"""
 		"""
-		return stats.median(self.values())
-
+		key_type = self.key_types_distribution().most_common(1)[0]
+		print(key_type)
+		if key_type[0] not in NUMBER_TYPES or key_type[1] != 1.0:
+			raise TypeError("Distribution is not a numerical type.")
+		else:
+			return stats.median(self.elements())
+		
 	def median_low(self):
 		"""
 		"""
-		return stats.median_low(self.values())
+		key_type = self.key_types_distribution().most_common(1)[0]
+		if key_type[0] not in NUMBER_TYPES or key_type[1] != 1.0:
+			raise TypeError("Distribution is not a numerical type.")
+		else:
+			return stats.median_low(self.elements())
 
 	def median_high(self):
 		"""
 		"""
-		return stats.median_high(self.values())
-
+		key_type = self.key_types_distribution().most_common(1)[0]
+		if key_type[0] not in NUMBER_TYPES or key_type[1] != 1.0:
+			raise TypeError("Distribution is not a numerical type.")
+		else:
+			return stats.median_high(self.elements())
+		
 	def median_grouped(self):
 		"""
 		"""
-		return stats.median_grouped(self.values())
-
+		key_type = self.key_types_distribution().most_common(1)[0]
+		if key_type[0] not in NUMBER_TYPES or key_type[1] != 1.0:
+			raise TypeError("Distribution is not a numerical type.")
+		else:	
+			return stats.median_grouped(self.elements())
+		
 	def mode(self):
 		"""
 		"""
-		return stats.mode(self.values())
+		return stats.mode(self.elements())
 
 	def variance(self):
 		"""
 		"""
-		return stats.variance(self.values())
+		return stats.variance(self.elements())
 
 	def pvariance(self):
 		"""
 		"""
-		return stats.pvariance(self.values())
+		return stats.pvariance(self.elements())
 
 	def stdev(self, ):
 		"""
 		"""
-		return stats.stdev(self.values())
+		return stats.stdev(self.elements())
 
 	def pstdev(self):
 		"""
 		"""
-		return stats.pstdev(self.values())
+		return stats.pstdev(self.elements())
 
 	def best_pair(self):
-		return self.most_common(1)[0]
-
+		try:
+			self.mode()
+		except (stats.StatisticsError):
+			raise MultipleMostCommonValuesError("Two or more values appear more than once.")
+		else:
+			return self.most_common(1)[0]
+		
 	def argmax(self):
 		"""
 		"""
diff --git a/tests/test_statscounter.py b/tests/test_statscounter.py
index fa551cd..dd028e7 100644
--- a/tests/test_statscounter.py
+++ b/tests/test_statscounter.py
@@ -1,56 +1,103 @@
 from __future__ import division
 from pytest import raises
 from statscounter import StatsCounter, stats
-
+from statscounter.statscounter import MultipleMostCommonValuesError
 
 class TestStatsCounter:
-	counter_ints = StatsCounter({str(s):s for s in range(1000)})
-
-	def test_mean_int(self):
-		m = self.counter_ints.mean()
-		d = 499500/1000
+	counter_ints = StatsCounter([1,1,2,3,4])
+	counter_ints_with_two_modes = StatsCounter([1,1,2,3,4,4])
+	counter_chars = StatsCounter('aabccd')
+	
+	def test_key_types_distribution(self):
+		ci = self.counter_ints.key_types_distribution()
+		ci2 = self.counter_ints_with_two_modes.key_types_distribution()
+		cc = self.counter_chars.key_types_distribution()
+		
+		assert ci == StatsCounter(['int'])
+		assert ci2 == StatsCounter(['int'])
+		assert cc == StatsCounter(['str']) 
+		
+	def test_mean(self):
+		m = self.counter_ints_with_two_modes.mean()
+		d = 15/6
 		assert m == d
-
+	
+	def test_mean_throws_exception(self):
+		with raises(TypeError):
+			self.counter_chars.mean()
+	
+	def test_median(self):
+		m = self.counter_ints_with_two_modes.median()
+		assert m == 2.5
+		
+	def test_median_throws_exception(self):
+		with raises(TypeError):
+			self.counter_chars.median()
+		
 	def test_median_low(self):
-		m = self.counter_ints.median_low()
-		assert m == 499
-
+		m = self.counter_ints_with_two_modes.median_low()
+		assert m == 2		
+	
+	def test_median_low_throws_exception(self):
+		with raises(TypeError):
+			self.counter_chars.median_low()
+	
 	def test_median_high(self, ):
-		m = self.counter_ints.median_high()
-		assert m == 500
+		m = self.counter_ints_with_two_modes.median_high()
+		assert m == 3
+		
+	def test_median_high_throws_exception(self):
+		with raises(TypeError):
+			self.counter_chars.median_high()
 
 	def test_median_grouped(self, ):
-		m = self.counter_ints.median_grouped()
-		assert m == 499.5
-
-	def test_mode(self):
+		m = self.counter_ints_with_two_modes.median_grouped()
+		assert m == 2.5
+		
+	def test_median_grouped_throws_exception(self):
+		with raises(TypeError):
+			self.counter_chars.median_grouped()	
+	
+	def test_mode(self, ):
+		m = self.counter_ints.mode()
+		assert m == 1
+		
+	def test_mode_throws_exception(self):
 		with raises(stats.StatisticsError):
-			self.counter_ints.mode()
+			self.counter_ints_with_two_modes.mode()
 
 	def test_variance(self):
-		m = self.counter_ints.variance()
-		assert m == 83416.66666666667
+		m = self.counter_ints_with_two_modes.variance()
+		assert m == 1.9
 
 	def test_stdev(self, ):
-		m = self.counter_ints.stdev()
-		assert m == 288.8194360957494
+		m = self.counter_ints_with_two_modes.stdev()
+		assert m == 1.378404875209022
 
 	def test_pvariance(self):
-		m = self.counter_ints.pvariance()
-		assert m == 83333.25
+		m = self.counter_ints_with_two_modes.pvariance()
+		assert m == 1.5833333333333333
 
 	def test_pstdev(self, ):
-		m = self.counter_ints.pstdev()
-		assert m == 288.6749902572095
-
+		m = self.counter_ints_with_two_modes.pstdev()
+		assert m == 1.2583057392117916
+	
 	def test_argmax(self):
 		m = self.counter_ints.argmax()
-		assert m == '999'
+		assert m == 1
+		
+	def test_argmax_throws_exception(self):
+		with raises(MultipleMostCommonValuesError):
+			m = self.counter_ints_with_two_modes.argmax()
 
 	def test_max(self):
 		m = self.counter_ints.max()
-		assert m == 999
+		assert m == 2
 
+	def test_max_throws_exception(self):
+		with raises(MultipleMostCommonValuesError):
+			m = self.counter_ints_with_two_modes.max()
+		
 	def test_normalize(self):
 		pdist = StatsCounter({1: 1, 2: 2, 3: 1}).normalize()
 		assert pdist == {