diff --git a/public/java/src/org/broadinstitute/sting/utils/recalibration/RecalDatumNode.java b/public/java/src/org/broadinstitute/sting/utils/recalibration/RecalDatumNode.java
index 62ea67d7c..3af91be16 100644
--- a/public/java/src/org/broadinstitute/sting/utils/recalibration/RecalDatumNode.java
+++ b/public/java/src/org/broadinstitute/sting/utils/recalibration/RecalDatumNode.java
@@ -2,7 +2,9 @@ package org.broadinstitute.sting.utils.recalibration;
 
 import com.google.java.contract.Ensures;
 import com.google.java.contract.Requires;
+import org.apache.commons.math.stat.inference.ChiSquareTestImpl;
 import org.apache.log4j.Logger;
+import org.broadinstitute.sting.utils.MathUtils;
 import org.broadinstitute.sting.utils.collections.Pair;
 
 import java.util.HashSet;
@@ -15,8 +17,9 @@ import java.util.Set;
  * @since 07/27/12
  */
 public class RecalDatumNode<T extends RecalDatum> {
+    private final static boolean USE_CHI2 = true;
     protected static Logger logger = Logger.getLogger(RecalDatumNode.class);
-    private final static double UNINITIALIZED = -1.0;
+    private final static double UNINITIALIZED = Double.NEGATIVE_INFINITY;
     private final T recalDatum;
     private double fixedPenalty = UNINITIALIZED;
     private final Set<RecalDatumNode<T>> subnodes;
@@ -56,11 +59,11 @@ public class RecalDatumNode<T extends RecalDatum> {
         if ( fixedPenalty != UNINITIALIZED )
             return fixedPenalty;
         else
-            return calcPenalty(recalDatum.getEmpiricalErrorRate());
+            return calcPenalty();
     }
 
     public double calcAndSetFixedPenalty(final boolean doEntireTree) {
-        fixedPenalty = calcPenalty(recalDatum.getEmpiricalErrorRate());
+        fixedPenalty = calcPenalty();
         if ( doEntireTree )
             for ( final RecalDatumNode<T> sub : subnodes )
                 sub.calcAndSetFixedPenalty(doEntireTree);
@@ -79,14 +82,23 @@ public class RecalDatumNode<T extends RecalDatum> {
         return subnodes.size();
     }
 
-    public double getMinNodePenalty() {
+    /**
+     * Total penalty is the sum of leaf node penalties
+     *
+     * This algorithm assumes that penalties have been fixed before pruning, as leaf nodes by
+     * definition have 0 penalty unless they represent a pruned tree with underlying -- but now
+     * pruned -- subtrees
+     *
+     * @return
+     */
+    public double totalPenalty() {
         if ( isLeaf() )
-            return Double.MAX_VALUE;
+            return getPenalty();
         else {
-            double minPenalty = getPenalty();
+            double sum = 0.0;
             for ( final RecalDatumNode<T> sub : subnodes )
-                minPenalty = Math.min(minPenalty, sub.getMinNodePenalty());
-            return minPenalty;
+                sum += sub.totalPenalty();
+            return sum;
         }
     }
 
@@ -97,6 +109,17 @@ public class RecalDatumNode<T extends RecalDatum> {
         return subMax + 1;
     }
 
+    public int minDepth() {
+        if ( isLeaf() )
+            return 1;
+        else {
+            int subMin = Integer.MAX_VALUE;
+            for ( final RecalDatumNode<T> sub : subnodes )
+                subMin = Math.min(subMin, sub.minDepth());
+            return subMin + 1;
+        }
+    }
+
     public int size() {
         int size = 1;
         for ( final RecalDatumNode<T> sub : subnodes )
@@ -104,6 +127,58 @@ public class RecalDatumNode<T extends RecalDatum> {
         return size;
     }
 
+    public int numLeaves() {
+        if ( isLeaf() )
+            return 1;
+        else {
+            int size = 0;
+            for ( final RecalDatumNode<T> sub : subnodes )
+                size += sub.numLeaves();
+            return size;
+        }
+    }
+
+    private double calcPenalty() {
+        if ( USE_CHI2 )
+            return calcPenaltyChi2();
+        else
+            return calcPenaltyLog10(getRecalDatum().getEmpiricalErrorRate());
+    }
+
+    private double calcPenaltyChi2() {
+        if ( isLeaf() )
+            return 0.0;
+        else {
+            final long[][] counts = new long[subnodes.size()][2];
+
+            int i = 0;
+            for ( RecalDatumNode<T> subnode : subnodes ) {
+                counts[i][0] = subnode.getRecalDatum().getNumMismatches();
+                counts[i][1] = subnode.getRecalDatum().getNumObservations();
+                i++;
+            }
+
+            final double chi2 = new ChiSquareTestImpl().chiSquare(counts);
+
+//            StringBuilder x = new StringBuilder();
+//            StringBuilder y = new StringBuilder();
+//            for ( int k = 0; k < counts.length; k++) {
+//                if ( k != 0 ) {
+//                    x.append(", ");
+//                    y.append(", ");
+//                }
+//                x.append(counts[k][0]);
+//                y.append(counts[k][1]);
+//            }
+//            logger.info("x = c(" + x.toString() + ")");
+//            logger.info("y = c(" + y.toString() + ")");
+//            logger.info("chi2 = " + chi2);
+
+            return chi2;
+            //return Math.log10(chi2);
+        }
+    }
+
     /**
      * Calculate the penalty of this interval, given the overall error rate for the interval
      *
@@ -119,7 +194,7 @@ public class RecalDatumNode<T extends RecalDatum> {
      */
     @Requires("globalErrorRate >= 0.0")
     @Ensures("result >= 0.0")
-    private double calcPenalty(final double globalErrorRate) {
+    private double calcPenaltyLog10(final double globalErrorRate) {
         if ( globalErrorRate == 0.0 ) // there were no observations, so there's no penalty
             return 0.0;
 
@@ -136,7 +211,7 @@ public class RecalDatumNode<T extends RecalDatum> {
         } else {
             double sum = 0;
             for ( final RecalDatumNode<T> hrd : subnodes)
-                sum += hrd.calcPenalty(globalErrorRate);
+                sum += hrd.calcPenaltyLog10(globalErrorRate);
             return sum;
         }
     }
@@ -173,17 +248,38 @@ public class RecalDatumNode<T extends RecalDatum> {
      * @return
      */
     private RecalDatumNode<T> removeLowestPenaltyNode() {
-        final RecalDatumNode<T> oneRemoved = removeFirstNodeWithPenalty(getMinNodePenalty()).getFirst();
+        final Pair<RecalDatumNode<T>, Double> nodeToRemove = getMinPenaltyNode();
+        logger.info("Removing " + nodeToRemove.getFirst() + " with penalty " + nodeToRemove.getSecond());
+
+        final Pair<RecalDatumNode<T>, Boolean> result = removeNode(nodeToRemove.getFirst());
+
+        if ( ! result.getSecond() )
+            throw new IllegalStateException("Never removed any node!");
+
+        final RecalDatumNode<T> oneRemoved = result.getFirst();
         if ( oneRemoved == null )
             throw new IllegalStateException("Removed our root node, wow, didn't expect that");
         return oneRemoved;
     }
 
-    private Pair<RecalDatumNode<T>, Boolean> removeFirstNodeWithPenalty(final double penaltyToRemove) {
-        if ( getPenalty() == penaltyToRemove ) {
-            logger.info("Removing " + this + " with penalty " + penaltyToRemove);
+    private Pair<RecalDatumNode<T>, Double> getMinPenaltyNode() {
+        final double myValue = isLeaf() ? Double.MAX_VALUE : getPenalty();
+        Pair<RecalDatumNode<T>, Double> maxNode = new Pair<RecalDatumNode<T>, Double>(this, myValue);
+
+        for ( final RecalDatumNode<T> sub : subnodes ) {
+            final Pair<RecalDatumNode<T>, Double> subFind = sub.getMinPenaltyNode();
+            if ( subFind.getSecond() < maxNode.getSecond() ) {
+                maxNode = subFind;
+            }
+        }
+
+        return maxNode;
+    }
+
+    private Pair<RecalDatumNode<T>, Boolean> removeNode(final RecalDatumNode<T> nodeToRemove) {
+        if ( this == nodeToRemove ) {
             if ( isLeaf() )
-                throw new IllegalStateException("Trying to remove a leaf node from the tree! " + this + " " + penaltyToRemove);
+                throw new IllegalStateException("Trying to remove a leaf node from the tree! " + this + " " + nodeToRemove);
             // node is the thing we are going to remove, but without any subnodes
             final RecalDatumNode<T> node = new RecalDatumNode<T>(getRecalDatum(), fixedPenalty);
             return new Pair<RecalDatumNode<T>, Boolean>(node, true);
@@ -200,7 +296,7 @@ public class RecalDatumNode<T extends RecalDatum> {
                     sub.add(sub1);
                 } else {
                     // haven't removed anything yet, so try
-                    final Pair<RecalDatumNode<T>, Boolean> maybeRemoved = sub1.removeFirstNodeWithPenalty(penaltyToRemove);
+                    final Pair<RecalDatumNode<T>, Boolean> maybeRemoved = sub1.removeNode(nodeToRemove);
                     removedSomething = maybeRemoved.getSecond();
                     sub.add(maybeRemoved.getFirst());
                 }