diff --git a/src/model/binary.rs b/src/model/binary.rs
index 0069be8..f69209d 100644
--- a/src/model/binary.rs
+++ b/src/model/binary.rs
@@ -147,7 +147,7 @@ impl Binary {
         false
     }
 
-    pub fn probabilities(&mut self, team_1: &[&str], team_2: &[&str], t: f64) -> (f64, f64) {
+    pub fn probabilities(&self, team_1: &[&str], team_2: &[&str], t: f64) -> (f64, f64) {
         let mut elems = self.process_items(team_1, 1.0);
         elems.extend(self.process_items(team_2, -1.0));
 
diff --git a/src/model/difference.rs b/src/model/difference.rs
index 1145503..c790373 100644
--- a/src/model/difference.rs
+++ b/src/model/difference.rs
@@ -83,7 +83,7 @@ impl DifferenceModel {
     }
 
     pub fn probabilities(
-        &mut self,
+        &self,
         _team_1: &[&str],
         _team_2: &[&str],
         _t: f64,
diff --git a/src/model/ternary.rs b/src/model/ternary.rs
index 7dae213..52a348f 100644
--- a/src/model/ternary.rs
+++ b/src/model/ternary.rs
@@ -165,7 +165,7 @@ impl TernaryModel {
     }
 
     pub fn probabilities(
-        &mut self,
+        &self,
         team_1: &[&str],
         team_2: &[&str],
         t: f64,