diff --git a/README.md b/README.md
index a4ac487..aa9b567 100644
--- a/README.md
+++ b/README.md
@@ -66,7 +66,7 @@ Supported formats include ISO-8601 application logs, syslog, nginx access logs,
 
 ## Evidence-backed reasoning
 
-The optional `--explain` flag turns existing detector output into concise, user-facing evidence statements. Each statement identifies its direct or statistical basis: parsed error level, message-length z-score with its configured threshold, or observed error count/rate in a complete analysis window. LogSight does not infer an incident root cause, use an LLM, send logs externally, or report a model-confidence score.
+The optional `--explain` flag turns existing detector output into concise, user-facing evidence statements. Each statement identifies its direct or statistical basis: parsed error level, message-length z-score with its configured threshold, or observed error count/rate in a complete analysis window. Each statement also reports a deterministic support level: `single-signal` for one detector signal and `corroborated` when the same entry meets both error-level and statistical criteria. LogSight does not infer an incident root cause, use an LLM, send logs externally, or report a model-confidence score.
 
 ```bash
 logsight analyze application.log --window 200 --spike-threshold 0.20 --explain
diff --git a/logsight/cli.py b/logsight/cli.py
index 2f4d62b..3db38c8 100644
--- a/logsight/cli.py
+++ b/logsight/cli.py
@@ -56,8 +56,8 @@ def _print_explanations(explanations: list[EvidenceExplanation]) -> None:
     for explanation in explanations:
         evidence = ", ".join(explanation.evidence)
         console.print(
-            f"  [{explanation.evidence_strength}] {escape(explanation.summary)} "
-            f"([dim]{escape(evidence)}[/dim])"
+            f"  support={explanation.evidence_strength};{explanation.support_level} — "
+            f"{escape(explanation.summary)} ({escape(evidence)})"
         )
 
 
diff --git a/logsight/reasoning.py b/logsight/reasoning.py
index d6bfdd9..aa19c07 100644
--- a/logsight/reasoning.py
+++ b/logsight/reasoning.py
@@ -12,6 +12,7 @@
 from logsight.analyzer import AnomalyReport, ErrorRateSpike
 
 EvidenceStrength = Literal["direct", "statistical"]
+SupportLevel = Literal["single-signal", "corroborated"]
 
 
 @dataclass(frozen=True)
@@ -21,6 +22,7 @@ class EvidenceExplanation:
     category: str
     summary: str
     evidence_strength: EvidenceStrength
+    support_level: SupportLevel
     evidence: tuple[str, ...]
 
 
@@ -42,6 +44,11 @@ def explain_report(
                         "no root cause is inferred."
                     ),
                     evidence_strength="direct",
+                    support_level=(
+                        "corroborated"
+                        if "message_length_zscore" in finding.reasons
+                        else "single-signal"
+                    ),
                     evidence=(
                         f"level={entry.level.value}",
                         f"message_length={len(entry.message)}",
@@ -57,6 +64,9 @@ def explain_report(
                         "statistical threshold; no root cause is inferred."
                     ),
                     evidence_strength="statistical",
+                    support_level=(
+                        "corroborated" if "error_level" in finding.reasons else "single-signal"
+                    ),
                     evidence=(
                         f"zscore={finding.message_length_zscore:.3f}",
                         f"threshold={report.zscore_threshold:.3f}",
@@ -74,6 +84,7 @@ def explain_report(
                     "threshold; no root cause is inferred."
                 ),
                 evidence_strength="statistical",
+                support_level="single-signal",
                 evidence=(
                     f"errors={spike.error_count}",
                     f"entries={spike.total}",
diff --git a/tests/test_cli.py b/tests/test_cli.py
index f37225e..16c742b 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -68,4 +68,5 @@ def test_explain_uses_detector_evidence(self, tmp_path):
         assert result.exit_code == 0
         assert "Evidence-backed findings" in result.output
         assert "level=ERROR" in result.output
+        assert "single-signal" in result.output
         assert "no root cause is inferred" in " ".join(result.output.split())
diff --git a/tests/test_reasoning.py b/tests/test_reasoning.py
index d1e6990..52f72ab 100644
--- a/tests/test_reasoning.py
+++ b/tests/test_reasoning.py
@@ -19,6 +19,7 @@ def test_explains_direct_error_evidence_without_causal_claim():
     assert len(explanations) == 1
     assert explanations[0].category == "error-level"
     assert explanations[0].evidence_strength == "direct"
+    assert explanations[0].support_level == "single-signal"
     assert "level=ERROR" in explanations[0].evidence
     assert "no root cause is inferred" in explanations[0].summary
 
@@ -48,3 +49,12 @@ def test_returns_no_explanations_when_detector_has_no_findings():
     report = detect_anomalies([_entry("INFO", "healthy")])
 
     assert explain_report(report) == []
+
+
+def test_marks_two_detector_signals_as_corroborated():
+    entries = [_entry("INFO", "normal")] * 20 + [_entry("ERROR", "x" * 500)]
+    report = detect_anomalies(entries, zscore_threshold=2.0)
+
+    explanations = explain_report(report)
+
+    assert any(item.support_level == "corroborated" for item in explanations)