diff --git a/src/Classification/DecisionTree.php b/src/Classification/DecisionTree.php
index 04cde56..b187796 100644
--- a/src/Classification/DecisionTree.php
+++ b/src/Classification/DecisionTree.php
@@ -386,9 +386,9 @@ class DecisionTree implements Classifier
                 $median = Mean::median($values);
                 foreach ($values as &$value) {
                     if ($value <= $median) {
-                        $value = "<= ${median}";
+                        $value = "<= {$median}";
                     } else {
-                        $value = "> ${median}";
+                        $value = "> {$median}";
                     }
                 }
             }
diff --git a/src/Classification/DecisionTree/DecisionTreeLeaf.php b/src/Classification/DecisionTree/DecisionTreeLeaf.php
index 04af3d6..3f8bd2c 100644
--- a/src/Classification/DecisionTree/DecisionTreeLeaf.php
+++ b/src/Classification/DecisionTree/DecisionTreeLeaf.php
@@ -122,7 +122,7 @@ class DecisionTreeLeaf
     public function getHTML(?array $columnNames = null): string
     {
         if ($this->isTerminal) {
-            $value = "<b>${this}->classValue</b>";
+            $value = "<b>{$this}->classValue</b>";
         } else {
             $value = $this->value;
             if ($columnNames !== null) {
@@ -132,13 +132,13 @@ class DecisionTreeLeaf
             }
 
             if ((bool) preg_match('/^[<>=]{1,2}/', (string) $value) === false) {
-                $value = "=${value}";
+                $value = "={$value}";
             }
 
-            $value = "<b>${col} ${value}</b><br>Gini: ".number_format($this->giniIndex, 2);
+            $value = "<b>{$col} {$value}</b><br>Gini: ".number_format($this->giniIndex, 2);
         }
 
-        $str = "<table ><tr><td colspan=3 align=center style='border:1px solid;'>${value}</td></tr>";
+        $str = "<table ><tr><td colspan=3 align=center style='border:1px solid;'>{$value}</td></tr>";
 
         if ($this->leftLeaf !== null || $this->rightLeaf !== null) {
             $str .= '<tr>';
diff --git a/src/Classification/Linear/DecisionStump.php b/src/Classification/Linear/DecisionStump.php
index 258939e..ae81d56 100644
--- a/src/Classification/Linear/DecisionStump.php
+++ b/src/Classification/Linear/DecisionStump.php
@@ -87,7 +87,7 @@ class DecisionStump extends WeightedClassifier
 
     public function __toString(): string
     {
-        return "IF ${this}->column ${this}->operator ${this}->value ".
+        return "IF {$this->column} {$this->operator} {$this->value} ".
             'THEN '.$this->binaryLabels[0].' '.
             'ELSE '.$this->binaryLabels[1];
     }
diff --git a/src/FeatureExtraction/StopWords.php b/src/FeatureExtraction/StopWords.php
index f5622fd..1b07410 100644
--- a/src/FeatureExtraction/StopWords.php
+++ b/src/FeatureExtraction/StopWords.php
@@ -25,7 +25,7 @@ class StopWords
 
     public static function factory(string $language = 'English'): self
     {
-        $className = __NAMESPACE__."\\StopWords\\${language}";
+        $className = __NAMESPACE__."\\StopWords\\{$language}";
 
         if (!class_exists($className)) {
             throw new InvalidArgumentException(sprintf('Can\'t find "%s" language for StopWords', $language));
diff --git a/src/Helper/OneVsRest.php b/src/Helper/OneVsRest.php
index 691fb64..b17fc02 100644
--- a/src/Helper/OneVsRest.php
+++ b/src/Helper/OneVsRest.php
@@ -157,7 +157,7 @@ trait OneVsRest
      */
     private function binarizeTargets(array $targets, $label): array
     {
-        $notLabel = "not_${label}";
+        $notLabel = "not_{$label}";
         foreach ($targets as $key => $target) {
             $targets[$key] = $target == $label ? $label : $notLabel;
         }