Index: xwiki-platform-core/xwiki-core/src/test/java/com/xpn/xwiki/criteria/impl/PeriodFactoryTest.java
===================================================================
--- xwiki-platform-core/xwiki-core/src/test/java/com/xpn/xwiki/criteria/impl/PeriodFactoryTest.java	(revision 0)
+++ xwiki-platform-core/xwiki-core/src/test/java/com/xpn/xwiki/criteria/impl/PeriodFactoryTest.java	(revision 0)
@@ -0,0 +1,69 @@
+/*
+ * See the NOTICE file distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation; either version 2.1 of
+ * the License, or (at your option) any later version.
+ *
+ * This software is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this software; if not, write to the Free
+ * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
+ * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
+ */
+package com.xpn.xwiki.criteria.impl;
+
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+
+import junit.framework.TestCase;
+
+import com.xpn.xwiki.stats.impl.xwiki.XWikiStatsReader;
+
+/**
+ * Unit tests for {@link PeriodFactory}.
+ */
+public class PeriodFactoryTest extends TestCase
+{
+    /**
+     * Tests if the start code of a day period is strictly less than its end code. This is needed
+     * because the {@link XWikiStatsReader} retrieves the statistics that have been recorded between
+     * the start code, including it, and the end code, excluding it.
+     */
+    public void testDayPeriodStartEndCode()
+    {
+        Period day = PeriodFactory.createDayPeriod(System.currentTimeMillis());
+        SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
+        try {
+            long start = sdf.parse(String.valueOf(day.getStartCode())).getTime();
+            long end = sdf.parse(String.valueOf(day.getEndCode())).getTime();
+            assertTrue("Start code must be less than end code", start < end);
+        } catch (ParseException e) {
+            assertTrue(e.getMessage(), false);
+        }
+    }
+
+    /**
+     * Tests if the start code of a month period is strictly less than its end code. This is needed
+     * because the {@link XWikiStatsReader} retrieves the statistics that have been recorded between
+     * the start code, including it, and the end code, excluding it.
+     */
+    public void testMonthPeriodStartEndCode()
+    {
+        Period month = PeriodFactory.createMonthPeriod(System.currentTimeMillis());
+        SimpleDateFormat sdf = new SimpleDateFormat("yyyyMM");
+        try {
+            long start = sdf.parse(String.valueOf(month.getStartCode())).getTime();
+            long end = sdf.parse(String.valueOf(month.getEndCode())).getTime();
+            assertTrue("Start code must be less than end code", start < end);
+        } catch (ParseException e) {
+            assertTrue(e.getMessage(), false);
+        }
+    }
+}
Index: xwiki-platform-core/xwiki-core/src/main/java/com/xpn/xwiki/stats/impl/xwiki/XWikiStatsReader.java
===================================================================
--- xwiki-platform-core/xwiki-core/src/main/java/com/xpn/xwiki/stats/impl/xwiki/XWikiStatsReader.java	(revision 9580)
+++ xwiki-platform-core/xwiki-core/src/main/java/com/xpn/xwiki/stats/impl/xwiki/XWikiStatsReader.java	(working copy)
@@ -142,7 +142,7 @@
      * 
      * @param action the action for which to retrieve statistics.
      * @param scope the set of documents to consider.
-     * @param period the period of time.
+     * @param period the period of time, including its start date but excluding its end date.
      * @param step the step used for sampling the period.
      * @param context the XWiki context.
      * @return a map of (date, actionCount) pairs.
@@ -183,7 +183,7 @@
      *            or "download". If the action is "view" then the documents are ordered by the
      *            number of times they have been viewed so far.
      * @param scope the set of documents for which to retrieve statistics.
-     * @param period the period of time.
+     * @param period the period of time, including its start date but excluding its end date.
      * @param range the sub-range to return from the entire result set. Use this parameter for
      *            pagination.
      * @param context the XWiki context.
@@ -205,7 +205,7 @@
         try {
             String query = MessageFormat.format(
                 "select name, sum(pageViews) from DocumentStats"
-                + " where {0} and action=? and ? <= period and period <= ? group by name order"
+                + " where {0} and action=? and ? <= period and period < ? group by name order"
                 + " by sum(pageViews) {1}", nameFilter, sortOrder);
 
             paramList.add(action);
@@ -260,7 +260,7 @@
      * 
      * @param domain the domain used for filtering the results.
      * @param scope the scope of referred documents for which to retrieve statistics.
-     * @param period the period of time.
+     * @param period the period of time, including its start date but excluding its end date.
      * @param range the sub-range to return from the entire result set. Use this parameter for
      *            pagination.
      * @param context the XWiki context.
@@ -281,7 +281,7 @@
         try {
             String query = MessageFormat.format(
                 "select name, sum(pageViews) from RefererStats"
-                + " where {0} and referer like ? and ? <= period and period <= ? group by name"
+                + " where {0} and referer like ? and ? <= period and period < ? group by name"
                 + " order by sum(pageViews) {1}", nameFilter, sortOrder);
 
             paramList.add(getHqlValidDomain(domain));
@@ -309,7 +309,7 @@
      * @param domain the domain for which to retrieve statistics. To retrieve statistics for all
      *            domains use the empty string.
      * @param scope the scope of referred documents to use for filtering the results.
-     * @param period the period of time.
+     * @param period the period of time, including its start date but excluding its end date.
      * @param range the sub-range to return from the entire result set. Use this parameter for
      *            pagination.
      * @param context the XWiki context.
@@ -330,7 +330,7 @@
         try {
             String query =
                 MessageFormat.format("select referer, sum(pageViews) from RefererStats"
-                    + " where {0} and referer like ? and ? <= period and period <= ?"
+                    + " where {0} and referer like ? and ? <= period and period < ?"
                     + " group by referer order by sum(pageViews) {1}", nameFilter, sortOrder);
 
             paramList.add(getHqlValidDomain(domain));
@@ -384,7 +384,7 @@
      * @param action the action the results should be ordered by. It can be one of: "view", "save"
      *            or "download". If the action is "view" then the visitors are ordered by the number
      *            of pages they have viewed so far.
-     * @param period the period of time.
+     * @param period the period of time, including its start date but excluding its end date.
      * @param range the sub-range to return from the entire result set. Use this parameter for
      *            pagination.
      * @param context the XWiki context.