diff --git a/Models/Answer.php b/Models/Answer.php
index 160a591..85fe848 100644
--- a/Models/Answer.php
+++ b/Models/Answer.php
@@ -31,7 +31,7 @@ class Answer
      * @var int
      * @since 1.0.0
      */
-    private $id = 0;
+    private int $id = 0;
 
     /**
      * Name.
@@ -39,7 +39,7 @@ class Answer
      * @var string
      * @since 1.0.0
      */
-    private $name = '';
+    private string $name = '';
 
     /**
      * Description.
@@ -47,7 +47,7 @@ class Answer
      * @var string
      * @since 1.0.0
      */
-    private $description = '';
+    private string $description = '';
 
     private static $instances = [];
 
diff --git a/Models/Question.php b/Models/Question.php
index b55ee78..e9eb8c2 100644
--- a/Models/Question.php
+++ b/Models/Question.php
@@ -31,7 +31,7 @@ class Question
      * @var int
      * @since 1.0.0
      */
-    private $id = 0;
+    private int $id = 0;
 
     /**
      * Name.
@@ -39,7 +39,7 @@ class Question
      * @var string
      * @since 1.0.0
      */
-    private $name = '';
+    private string $name = '';
 
     /**
      * Description.
@@ -47,7 +47,7 @@ class Question
      * @var string
      * @since 1.0.0
      */
-    private $description = '';
+    private string $description = '';
 
     private static $instances = [];
 
diff --git a/Models/Section.php b/Models/Section.php
index 7777399..db1a958 100644
--- a/Models/Section.php
+++ b/Models/Section.php
@@ -31,7 +31,7 @@ class Section
      * @var int
      * @since 1.0.0
      */
-    private $id = 0;
+    private int $id = 0;
 
     /**
      * Name.
@@ -39,7 +39,7 @@ class Section
      * @var string
      * @since 1.0.0
      */
-    private $name = '';
+    private string $name = '';
 
     /**
      * Description.
@@ -47,7 +47,7 @@ class Section
      * @var string
      * @since 1.0.0
      */
-    private $description = '';
+    private string $description = '';
 
     private static $instances = [];
 
diff --git a/Models/Survey.php b/Models/Survey.php
index b4756c1..a56825d 100644
--- a/Models/Survey.php
+++ b/Models/Survey.php
@@ -31,7 +31,7 @@ class Survey
      * @var int
      * @since 1.0.0
      */
-    private $id = 0;
+    private int $id = 0;
 
     /**
      * Name.
@@ -39,7 +39,7 @@ class Survey
      * @var string
      * @since 1.0.0
      */
-    private $name = '';
+    private string $name = '';
 
     /**
      * Description.
@@ -47,7 +47,7 @@ class Survey
      * @var string
      * @since 1.0.0
      */
-    private $description = '';
+    private string $description = '';
 
     /**
      * Created.
@@ -63,7 +63,7 @@ class Survey
      * @var int
      * @since 1.0.0
      */
-    private $creator = null;
+    private int $creator = null;
 
     private static $instances = [];