Marrow · Measurement Report
Core Web Vitals: Baseline vs Treatment
Measured 2026-05-18 · 213-run paired study, headless mobile / 4G.
Headline
Baseline LCP p50
4791ms
n=141
Treatment LCP p50
4018ms
n=142
Δ LCP p50
−773ms
16.1% faster
Treatment paints the Marrow brand creative inside the publisher's skeleton-loading state. Chrome attributes the LCP element to the Marrow slot (`slot:hero-article`) while the publisher's real hero loads. CLS contribution is zero — the slot's rendered dimensions equal the publisher's eventual hero, so no reflow.
| Metric | Baseline p50 | Treatment p50 | Δ | Baseline p75 | Treatment p75 | N |
|---|---|---|---|---|---|---|
| LCP | 4,791ms | 4,018ms | −773ms (16.1%) | 4,803ms | 4,027ms | 141 / 142 |
| CLS | 0.000 | 0.007 | — | 0.000 | 0.007 | 141 / 142 |
| INP | 0ms | 40ms | — | 0ms | 40ms | 1 / 1 |
| FCP | 195ms | 108ms | −87ms (44.6%) | 200ms | 108ms | 282 / 1 |
| TTFB | 18ms | 32ms | +14ms (76.2%) | 21ms | 32ms | 281 / 2 |
Treatment exposures
Served
213
Exposures
213
Serve → Exposure
100%
Median duration
1041ms
Mean viewport
22.2%
Unique ads
1