From d891b1d46c668cf1211db9e7a43dff9c1affa826 Mon Sep 17 00:00:00 2001
From: Tudor Sitaru <tudor.sitaru@gmail.com>
Date: Tue, 6 Jan 2026 15:49:57 +0000
Subject: [PATCH] standard deviation for comparison table

---
 frontend/app.js | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/frontend/app.js b/frontend/app.js
index cbf42cd..eb8c1cc 100644
--- a/frontend/app.js
+++ b/frontend/app.js
@@ -468,7 +468,6 @@ async function updateComparisonChart() {
 }
 
 function updateComparisonTable(comparison, metric, years) {
-    const firstYear = years[0];
     const lastYear = years[years.length - 1];
     const prevYear = years.length > 1 ? years[years.length - 2] : null;
     
@@ -477,11 +476,11 @@ function updateComparisonTable(comparison, metric, years) {
     years.forEach(year => {
         headerHtml += `<th>${year}</th>`;
     });
-    if (prevYear && prevYear !== firstYear) {
+    if (prevYear) {
         headerHtml += `<th title="Change from ${prevYear} to ${lastYear}">Δ 1yr</th>`;
     }
-    if (years.length > 1) {
-        headerHtml += `<th title="Change from ${firstYear} to ${lastYear}">Δ ${firstYear}→${lastYear}</th>`;
+    if (years.length > 2) {
+        headerHtml += `<th title="Standard deviation of scores (lower = more consistent)">Variability</th>`;
     }
     elements.tableHeader.innerHTML = headerHtml;
     
@@ -496,7 +495,6 @@ function updateComparisonTable(comparison, metric, years) {
             yearlyMap[d.year] = d[metric];
         });
         
-        const firstValue = yearlyMap[firstYear];
         const lastValue = yearlyMap[lastYear];
         const prevValue = prevYear ? yearlyMap[prevYear] : null;
         
@@ -505,10 +503,16 @@ function updateComparisonTable(comparison, metric, years) {
         const oneYearChangeStr = oneYearChange !== null ? oneYearChange.toFixed(1) : 'N/A';
         const oneYearClass = oneYearChange !== null ? (oneYearChange >= 0 ? 'positive' : 'negative') : '';
         
-        // Calculate total change
-        const totalChange = firstValue != null && lastValue != null ? (lastValue - firstValue) : null;
-        const totalChangeStr = totalChange !== null ? totalChange.toFixed(1) : 'N/A';
-        const totalChangeClass = totalChange !== null ? (totalChange >= 0 ? 'positive' : 'negative') : '';
+        // Calculate variability (standard deviation) - exclude null/0 values
+        const values = years.map(y => yearlyMap[y]).filter(v => v != null && v !== 0);
+        let variabilityStr = 'N/A';
+        if (values.length >= 2) {
+            const mean = values.reduce((a, b) => a + b, 0) / values.length;
+            const squaredDiffs = values.map(v => Math.pow(v - mean, 2));
+            const variance = squaredDiffs.reduce((a, b) => a + b, 0) / values.length;
+            const stdDev = Math.sqrt(variance);
+            variabilityStr = '±' + stdDev.toFixed(1);
+        }
         
         const color = CHART_COLORS[index % CHART_COLORS.length];
         
@@ -518,11 +522,11 @@ function updateComparisonTable(comparison, metric, years) {
             const value = yearlyMap[year];
             bodyHtml += `<td>${value != null ? formatMetricValue(value, metric) : '-'}</td>`;
         });
-        if (prevYear && prevYear !== firstYear) {
+        if (prevYear) {
             bodyHtml += `<td class="${oneYearClass}">${oneYearChangeStr !== 'N/A' ? (oneYearChange >= 0 ? '+' : '') + oneYearChangeStr : oneYearChangeStr}</td>`;
         }
-        if (years.length > 1) {
-            bodyHtml += `<td class="${totalChangeClass}">${totalChangeStr !== 'N/A' ? (totalChange >= 0 ? '+' : '') + totalChangeStr : totalChangeStr}</td>`;
+        if (years.length > 2) {
+            bodyHtml += `<td>${variabilityStr}</td>`;
         }
         bodyHtml += `</tr>`;
     });