diff --git a/core/opl/data.py b/core/opl/data.py
index 19c6705..5852514 100644
--- a/core/opl/data.py
+++ b/core/opl/data.py
@@ -142,7 +142,7 @@ def percentile(data, percent):
     if not data:
         return None
 
-    data.sort()
+    data = sorted(data)
     k = (len(data) - 1) * percent / 100
     # Python 2.x returns float for floor an ceil, so cast to int
     f = int(math.floor(k))
@@ -226,6 +226,7 @@ def data_stats(data):
             else 0.0,
             "stdev": statistics.stdev(data) if len(data) > 1 else 0.0,
             "range": max(data) - min(data),
+            "change": data[-1] - data[0],
             "percentile25": q25,
             "percentile75": q75,
             "percentile90": q90,
@@ -240,6 +241,7 @@ def data_stats(data):
             "max": max(data),
             "mean": (max(data) - min(data)) / len(data),
             "range": max(data) - min(data),
+            "change": data[-1] - data[0],
         }
     else:
         raise Exception(f"Do not know how to get stats for list of {type(data[0])}")
diff --git a/opl/data.py b/opl/data.py
index 19c6705..5852514 100644
--- a/opl/data.py
+++ b/opl/data.py
@@ -142,7 +142,7 @@ def percentile(data, percent):
     if not data:
         return None
 
-    data.sort()
+    data = sorted(data)
     k = (len(data) - 1) * percent / 100
     # Python 2.x returns float for floor an ceil, so cast to int
     f = int(math.floor(k))
@@ -226,6 +226,7 @@ def data_stats(data):
             else 0.0,
             "stdev": statistics.stdev(data) if len(data) > 1 else 0.0,
             "range": max(data) - min(data),
+            "change": data[-1] - data[0],
             "percentile25": q25,
             "percentile75": q75,
             "percentile90": q90,
@@ -240,6 +241,7 @@ def data_stats(data):
             "max": max(data),
             "mean": (max(data) - min(data)) / len(data),
             "range": max(data) - min(data),
+            "change": data[-1] - data[0],
         }
     else:
         raise Exception(f"Do not know how to get stats for list of {type(data[0])}")
diff --git a/tests/test_data.py b/tests/test_data.py
index 0006863..7281500 100644
--- a/tests/test_data.py
+++ b/tests/test_data.py
@@ -14,6 +14,7 @@ def test_data_stats(self):
         self.assertEqual(stats["mean"], 1)
         self.assertEqual(stats["max"], 2)
         self.assertEqual(stats["range"], 2)
+        self.assertEqual(stats["change"], 0)
         self.assertEqual(stats["percentile25"], 0.75)
         self.assertEqual(stats["percentile75"], 1.25)
         self.assertEqual(stats["iqr"], 0.5)
@@ -46,6 +47,7 @@ def test_data_stats_datetime(self):
             datetime.datetime.fromisoformat("2021-03-22T11:00:00.000000+00:00"),
         )
         self.assertEqual(stats["range"].total_seconds(), 3600)
+        self.assertEqual(stats["change"].total_seconds(), -3600)
 
     def test_data_stats_strange(self):
         data = [
@@ -99,3 +101,11 @@ def test_get_rps(self):
         rps_vals = opl.data.get_rps([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
         self.assertEqual(len(rps_vals), 5)
         self.assertEqual(sum(rps_vals) / len(rps_vals), 1.0)
+
+    def test_percentile(self):
+        data = [0, 1, 1, 2, 2, 1, 1, 0]
+        perc25 = opl.data.percentile(data, 25)
+        perc75 = opl.data.percentile(data, 75)
+        self.assertEqual(data, [0, 1, 1, 2, 2, 1, 1, 0])   # make sure data is not reordered
+        self.assertEqual(perc25, 0.75)
+        self.assertEqual(perc75, 1.25)