Improve SPRT Calculator

Allows specifying Alpha and Beta

Co-Authored-By: Gahtan Nahdi <[email protected]>

server/montytest/static/js/calc.js

@@ -6,6 +6,8 @@ const defaultParameters = {
   "elo-1": "2.0",
   "draw-ratio": "0.49",
   "rms-bias": "191",
+  alpha: "0.05",
+  beta: "0.05",
 };
 
 let validSprt = null;
@@ -64,10 +66,19 @@ function drawCharts(resize) {
   let elo1 = parseFloat(document.getElementById("elo-1").value);
   const drawRatio = parseFloat(document.getElementById("draw-ratio").value);
   const rmsBias = parseFloat(document.getElementById("rms-bias").value);
+  let alpha = parseFloat(document.getElementById("alpha").value);
+  let beta = parseFloat(document.getElementById("beta").value);
   let error = "";
   let sprt = null;
 
-  if (isNaN(elo0) || isNaN(elo1) || isNaN(drawRatio) || isNaN(rmsBias)) {
+  if (
+    isNaN(elo0) ||
+    isNaN(elo1) ||
+    isNaN(drawRatio) ||
+    isNaN(rmsBias) ||
+    isNaN(alpha) ||
+    isNaN(beta)
+  ) {
     error = "Unreadable input.";
   } else if (elo1 < elo0 + 0.5) {
     error = "The difference between Elo1 and Elo0 must be at least 0.5.";
@@ -77,8 +88,12 @@ function drawCharts(resize) {
     error = "The draw ratio must be strictly between 0.0 and 1.0.";
   } else if (rmsBias < 0) {
     error = "The RMS bias must be positive.";
+  } else if (alpha <= 0.0 || alpha >= 1.0 || beta <= 0.0 || beta >= 1.0) {
+    error = "The value of alpha and beta must be strictly between 0.0 and 1.0.";
+  } else if (alpha + beta >= 1.0) {
+    error = "The sum of alpha and beta must be strictly below 1.0";
   } else {
-    sprt = new Sprt(0.05, 0.05, elo0, elo1, drawRatio, rmsBias, eloModel);
+    sprt = new Sprt(alpha, beta, elo0, elo1, drawRatio, rmsBias, eloModel);
     if (sprt.variance <= 0) {
       error = "The draw ratio and the RMS bias are not compatible.";
     }
@@ -101,7 +116,7 @@ function drawCharts(resize) {
   history.replaceState(
     null,
     "",
-    `/sprt_calc?elo-model=${eloModel}&elo-0=${elo0}&elo-1=${elo1}&draw-ratio=${drawRatio}&rms-bias=${rmsBias}`,
+      `/sprt_calc?elo-model=${eloModel}&elo-0=${elo0}&elo-1=${elo1}&draw-ratio=${drawRatio}&rms-bias=${rmsBias}&alpha=${alpha}&beta=${beta}`,
   );
   elo0 = sprt.elo0;
   elo1 = sprt.elo1;

server/montytest/templates/sprt_calc.mak

@@ -55,6 +55,28 @@
       type="number"
       min="0"
     >
+  </div>
+    <div class="col-6 col-md-auto mb-3">
+    <label for="alpha" class="form-label">Alpha</label>
+    <input
+      id="alpha"
+      class="form-control number no-arrows"
+      type="number"
+      step="0.01"
+      min="0"
+      max="1"
+    >
+  </div>
+  <div class="col-6 col-md-auto mb-3">
+    <label for="beta" class="form-label">Beta</label>
+    <input
+      id="beta"
+      class="form-control number no-arrows"
+      type="number"
+      step="0.01"
+      min="0"
+      max="1"
+    >
   </div>
   <div class="col-12 col-md-auto mb-3 d-flex align-items-end">
     <input
@@ -79,10 +101,11 @@
       <a href="https://en.wikipedia.org/wiki/Sequential_probability_ratio_test"
         >SPRT test</a
       >
-      with &alpha;=&beta;=0.05. In other words, if the true Elo is less than
-      Elo0 then the probability of the test passing is less than 5%. On the
+      with error probabilities &alpha; and &beta;. If the true Elo is less than
+      Elo0 then the probability of the test passing is less than &alpha;. On the
+      other hand if the true Elo is more than Elo1 then the pass probability is
       other hand if the true Elo is more than Elo1 then the pass probability is
-      more than 95%.
+      more than (1-&beta;).
     </li>
     <li>
       If the Elo model is <b>Logistic</b> then the pass/fail probabilities are