diff --git a/apps/portal/src/pages/Statistics.stories.tsx b/apps/portal/src/pages/Statistics.stories.tsx
new file mode 100644
index 000000000..11297be81
--- /dev/null
+++ b/apps/portal/src/pages/Statistics.stories.tsx
@@ -0,0 +1,47 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+import type { Meta, StoryObj } from "@storybook/react-vite";
+import { expect } from "storybook/test";
+
+import { PerformanceTable } from "./Statistics";
+import type { AnalysisResponse } from "@/types";
+
+const analysis: AnalysisResponse = {
+  groups: [{
+    task: "Build a small API",
+    taskPromptId: "task-1",
+    workerType: "coder-acp-copilot",
+    total: 4,
+    completed: 4,
+    passed: 3,
+    rejected: 0,
+    passAtK: { 1: 0.75 },
+    successAtT: [0.5, 0.75],
+    iterationStats: { mean: 2, stdDev: 0.8, min: 1, max: 3 },
+    durationStats: { mean: 90_000, stdDev: 30_000, min: 60_000, max: 120_000 },
+  }],
+  kValues: [1],
+  maxT: 3,
+  summary: { totalRuns: 4, completedRuns: 4, passedRuns: 3, overallPassRate: 0.75, avgIterationsToPass: 2 },
+  availableCriteria: [],
+  selectedCriteria: [],
+  availableFeatures: [],
+  selectedFeatures: [],
+};
+
+const meta = {
+  component: PerformanceTable,
+  args: { data: analysis },
+} satisfies Meta<typeof PerformanceTable>;
+
+export default meta;
+type Story = StoryObj<typeof meta>;
+
+export const WithVariation: Story = {
+  play: async ({ canvas }) => {
+    await expect(canvas.getByText("Mean 2.0")).toBeVisible();
+    await expect(canvas.getByText("Std dev 0.8")).toBeVisible();
+    await expect(canvas.getByText("Std dev 30s")).toBeVisible();
+  },
+};
diff --git a/apps/portal/src/pages/Statistics.tsx b/apps/portal/src/pages/Statistics.tsx
index 2226adea8..0ffdded77 100644
--- a/apps/portal/src/pages/Statistics.tsx
+++ b/apps/portal/src/pages/Statistics.tsx
@@ -428,7 +428,7 @@ function InsightsRow({ insights }: { insights: DerivedInsights }) {
 
 // ─── Performance breakdown (merged iteration + duration) ────────────────────
 
-function PerformanceTable({ data }: { data: AnalysisResponse }) {
+export function PerformanceTable({ data }: { data: AnalysisResponse }) {
   const { groups } = data;
 
   if (groups.length === 0) {
@@ -472,8 +472,9 @@ function PerformanceTable({ data }: { data: AnalysisResponse }) {
           Performance by task & worker
         </CardTitle>
         <CardDescription>
-          Pass rate, iteration distribution, and run duration — sorted by pass
-          rate.
+          Pass rate and run variation, sorted by pass rate. Mean and standard
+          deviation use passed runs only; standard deviation shows how much
+          individual runs vary from the mean.
         </CardDescription>
       </CardHeader>
       <CardContent>
@@ -484,8 +485,8 @@ function PerformanceTable({ data }: { data: AnalysisResponse }) {
               <TableHead>Worker</TableHead>
               <TableHead className="text-center">Runs</TableHead>
               <TableHead className="w-[200px]">Pass rate</TableHead>
-              <TableHead className="text-center">Avg iter</TableHead>
-              <TableHead className="text-center">Avg duration</TableHead>
+              <TableHead className="text-center">Iterations to pass</TableHead>
+              <TableHead className="text-center">Run duration</TableHead>
               <TableHead className="w-[1%]" />
             </TableRow>
           </TableHeader>
@@ -551,22 +552,20 @@ function PerformanceTable({ data }: { data: AnalysisResponse }) {
                   </TableCell>
                   <TableCell className="text-center font-mono tabular-nums text-xs">
                     {group.iterationStats ? (
-                      <span
-                        title={`min ${group.iterationStats.min} · max ${group.iterationStats.max} · σ ${formatNumber(group.iterationStats.stdDev)}`}
-                      >
-                        {formatNumber(group.iterationStats.mean)}
-                      </span>
+                      <div title={`Minimum ${group.iterationStats.min} · Maximum ${group.iterationStats.max}`}>
+                        <span className="block">Mean {formatNumber(group.iterationStats.mean)}</span>
+                        <span className="block text-muted-foreground">Std dev {formatNumber(group.iterationStats.stdDev)}</span>
+                      </div>
                     ) : (
                       <span className="text-muted-foreground">—</span>
                     )}
                   </TableCell>
                   <TableCell className="text-center font-mono tabular-nums text-xs">
                     {group.durationStats ? (
-                      <span
-                        title={`min ${formatDuration(group.durationStats.min)} · max ${formatDuration(group.durationStats.max)} · σ ${formatDuration(group.durationStats.stdDev)}`}
-                      >
-                        {formatDuration(group.durationStats.mean)}
-                      </span>
+                      <div title={`Minimum ${formatDuration(group.durationStats.min)} · Maximum ${formatDuration(group.durationStats.max)}`}>
+                        <span className="block">Mean {formatDuration(group.durationStats.mean)}</span>
+                        <span className="block text-muted-foreground">Std dev {formatDuration(group.durationStats.stdDev)}</span>
+                      </div>
                     ) : (
                       <span className="text-muted-foreground">—</span>
                     )}
diff --git a/docs/architecture/app-design.md b/docs/architecture/app-design.md
index f1a243262..9366dbef5 100644
--- a/docs/architecture/app-design.md
+++ b/docs/architecture/app-design.md
@@ -702,6 +702,11 @@ The Statistics page (`apps/portal/src/pages/Statistics.tsx`) is backed by `GET /
 | `criteria` | Success criteria (comma-separated `criterionId`s) | A run counts as a pass only if **all** selected criteria pass; runs lacking a selected criterion are excluded |
 | `features` | Task prompt features (comma-separated `featureId`s) | Keep a run iff its task prompt was **detected** to have **every** selected feature (AND) |
 
+The performance table labels each passed-run distribution with its mean and
+standard deviation. Iteration statistics describe iterations to pass; duration
+statistics sum the measured turn durations for each passed run. Missing values
+appear when no passed run has the required measurement.
+
 The response exposes the option lists and current selection for each filter so the Portal can render filter bars: `availableCriteria` / `selectedCriteria` and `availableFeatures` / `selectedFeatures`. Both `available*` lists are computed over the full valid-run set **before** filtering, so the bars stay populated even when a filter combination matches zero runs (the Portal then shows a "no runs match" empty state instead of the "no data yet" state).
 
 **Detected-based feature semantics (intentional divergence).** A task prompt's `features[]` stores a `{featureId, detected}` row for *every* evaluated feature, so presence is near-universal and meaningless as a filter. `availableFeatures` is therefore the sorted union of featureIds with `detected === true` across valid runs, and the feature filter matches on `detected === true`. This is deliberately stricter than the MDP route (`GET /api/v1/criteria/mdp`), whose feature filter is presence-based. Runs join to task prompts by effective id (`taskPromptId || computeTaskPromptId(scenario.task)`) so legacy runs without a stored `taskPromptId` still resolve their features.