diff --git a/src/main/scala/esmeta/es/util/fuzzer/FSTree.scala b/src/main/scala/esmeta/es/util/fuzzer/FSTree.scala
index 9fa10c9885..bfc615342f 100644
--- a/src/main/scala/esmeta/es/util/fuzzer/FSTree.scala
+++ b/src/main/scala/esmeta/es/util/fuzzer/FSTree.scala
@@ -63,6 +63,8 @@ class FSTreeWrapper(
 ) {
   val fixedSensMap = MMap.empty[List[String], Int]
   var root: FSTree = FSTree(status = FSTreeStatus.Noticed, depth = 0)
+  var rootHits: Long = 0
+  var rootMisses: Long = 0
 
   def sensDistr: Map[Int, Int] =
     root.stacks.groupBy(_.size).transform((_, v) => v.size).withDefault(_ => 0)
@@ -107,6 +109,7 @@ class FSTreeWrapper(
       stacks.foreach { s =>
         root.touchByStack(s.take(config.maxSensitivity), isHit = true)
       }
+      rootHits += stacks.size
     MinifyFuzz.sampler("FSTree.touch") += System.currentTimeMillis() - startTime
 
   /** Insert feature stacks from a single script into the tree. The script
@@ -122,6 +125,7 @@ class FSTreeWrapper(
       stacks.foreach { s =>
         root.touchByStack(s.take(config.maxSensitivity), isHit = false)
       }
+      rootMisses += stacks.size
     MinifyFuzz.sampler("FSTree.touch") += System.currentTimeMillis() - startTime
 
   def apply(stack: List[String]): Int =
@@ -202,7 +206,12 @@ class FSTreeWrapper(
       isHit: Boolean,
     ): Unit =
       if isHit then hits += 1 else misses += 1
-      updateMyChiSqValue()
+
+      if (config.useLocalCorrelation)
+        updateMyLocalChiSqValue()
+      else
+        updateMyGlobalChiSqValue()
+
       updateMyStatus()
 
       stack match {
@@ -221,7 +230,7 @@ class FSTreeWrapper(
           }
       }
 
-    private def updateMyChiSqValue(): Unit =
+    private def updateMyLocalChiSqValue(): Unit =
       chiSqValue = computeFeatureChiSq(
         hits = hits,
         misses = misses,
@@ -229,6 +238,14 @@ class FSTreeWrapper(
         pMisses = parentMisses,
       )
 
+    private def updateMyGlobalChiSqValue(): Unit =
+      chiSqValue = computeFeatureChiSq(
+        hits = hits,
+        misses = misses,
+        pHits = rootHits,
+        pMisses = rootMisses,
+      )
+
     private def updateMyStatus(): Unit =
       status match {
         case Noticed =>
@@ -344,6 +361,7 @@ case class FSTreeConfig(
   oneSided: Boolean = true,
   isSelective: Boolean = true,
   useSrv: Boolean = true,
+  useLocalCorrelation: Boolean = false,
 )
 
 /** Status of a node in the tree
diff --git a/src/main/scala/esmeta/es/util/fuzzer/Fuzzer.scala b/src/main/scala/esmeta/es/util/fuzzer/Fuzzer.scala
index fcb5dab90d..26e42dea1b 100644
--- a/src/main/scala/esmeta/es/util/fuzzer/Fuzzer.scala
+++ b/src/main/scala/esmeta/es/util/fuzzer/Fuzzer.scala
@@ -278,7 +278,6 @@ class Fuzzer(
       BuiltinSynthesizer(cfg.spec.algorithms).initPool
         .map(BuiltinSynthesizer(cfg.spec.algorithms).name -> _),
     )
-    .take(42)
 
   lazy val logDir: String = s"$FUZZ_LOG_DIR/fuzz-$dateStr"
   lazy val symlink: String = s"$FUZZ_LOG_DIR/recent"
diff --git a/src/main/scala/esmeta/phase/Fuzz.scala b/src/main/scala/esmeta/phase/Fuzz.scala
index 74f77cee0d..a9b27945dc 100644
--- a/src/main/scala/esmeta/phase/Fuzz.scala
+++ b/src/main/scala/esmeta/phase/Fuzz.scala
@@ -9,7 +9,6 @@ import esmeta.es.*
 import esmeta.es.util.fuzzer.{Fuzzer, FSTreeConfig}
 import esmeta.es.util.{UnitWalker, Coverage, ValidityChecker}
 import esmeta.spec.util.GrammarGraph
-import esmeta.synthesizer.{SimpleSynthesizer, BuiltinSynthesizer}
 import scala.collection.mutable.ArrayBuffer
 
 /** `fuzz` phase */
diff --git a/src/main/scala/esmeta/phase/MinifyFuzz.scala b/src/main/scala/esmeta/phase/MinifyFuzz.scala
index 9b4f120c8c..e5f6b75d92 100644
--- a/src/main/scala/esmeta/phase/MinifyFuzz.scala
+++ b/src/main/scala/esmeta/phase/MinifyFuzz.scala
@@ -52,10 +52,14 @@ case object MinifyFuzz extends Phase[CFG, Coverage] {
         minTouch = config.fsMinTouch,
         oneSided = config.oneSided,
         isSelective = config.isSelectiveOpt
-          .getOrElse(
-            throw new Exception("sensitivity type is not set"),
-          ),
+          .getOrElse {
+            println(
+              "Sensitivity type is not set. Use selective by default.",
+            )
+            true
+          },
         useSrv = config.useSrv,
+        useLocalCorrelation = config.useLocalCorrelation,
       ),
       keepBugs = config.keepBugs,
       minifyCmd = config.minifier,
@@ -194,6 +198,18 @@ case object MinifyFuzz extends Phase[CFG, Coverage] {
       BoolOption(c => c.useSrv = false),
       "use the CLI to transpile scripts (default: server).",
     ),
+    (
+      "correlation-type",
+      StrOption((c, s) =>
+        c.useLocalCorrelation = s match {
+          case "local"  => true
+          case "global" => false
+          case _ =>
+            error("invalid correlation type: please set local or global")
+        },
+      ),
+      "set the correlation type: local or global",
+    ),
   )
   case class Config(
     var log: Boolean = false,
@@ -216,5 +232,6 @@ case object MinifyFuzz extends Phase[CFG, Coverage] {
     var minifier: Option[String] = None,
     var onlineTest: Boolean = false,
     var useSrv: Boolean = true,
+    var useLocalCorrelation: Boolean = false,
   )
 }