diff --git a/review/stats.py b/review/stats.py
index 89e341a..472a175 100644
--- a/review/stats.py
+++ b/review/stats.py
@@ -11,7 +11,7 @@ class ReviewData:
 
 
 class Board:
-    def __init__(self, datas):
+    def __init__(self, datas={}):
         self.datas = {}
         self.init(datas)
 
@@ -34,43 +34,46 @@ class Board:
 
     @property
     def min(self):
-        if self.datas == []:
+        if self.datas == {}:
             return 0
-        return min(self.datas.values())
+        return min(self.datas.keys())
 
     @property
     def max(self):
-        if self.datas == []:
+        if self.datas == {}:
             return 0
-        return max(self.datas.values())
+        return max(self.datas.keys())
 
     @property
     def avg(self):
-        if self.datas == []:
+        if self.datas == {}:
             return 0
-        return self.sum / len(self.datas)
+        return self.sum / sum(self.datas.values())
 
     @property
     def sum(self):
-        if self.datas == []:
-            return 0
-        return sum(self.datas.values())
+        result = 0
+        for data in self.datas:
+            result += self.datas[data] * data
+        return result
 
 
 class UserBoard(Board):
     def init(self, datas):
         for data in datas:
-            if data.user_count not in self.datas:
-                self.datas[data.user_count] = 0
-            self.datas[data.user_count] += 1
+            if data.user_count is not None:
+                if data.user_count not in self.datas:
+                    self.datas[data.user_count] = 0
+                self.datas[data.user_count] += 1
 
 
 class DurationBoard(Board):
     def init(self, datas):
         for data in datas:
-            if data.duration not in self.datas:
-                self.datas[data.duration] = 0
-            self.datas[data.duration] += 1
+            if data.duration is not None:
+                if data.duration not in self.datas:
+                    self.datas[data.duration] = 0
+                self.datas[data.duration] += 1
 
 
 class ReviewStats:
@@ -159,7 +162,7 @@ class ReviewStats:
                                 ReviewData(
                                     datetime.strptime(datas[0], "%Y%m%d-%Hh%M"),
                                     int(datas[1]),
-                                    int(datas[2]),
+                                    int(datas[2]) if datas[2]!="" else None,
                                 )
                             )
         except FileNotFoundError: