www.cdc.gov: History & Trends
How this site has changed over time. The weekly overview answers "what should I fix now?"; this page answers "how are we trending?"
Tracking since 2026-W24 — 17 weeks recorded. Accessibility score is stable (+0 pts since 2026-W36). Download the full trend series: CSV · JSON.
How the latest week compares
Latest week (2026-W40) vs. earlier look-back windows. positive/negative is relative to each measure — coloured by better or worse
| Measure | Now | vs 4 wk ago | vs 13 wk ago |
|---|
| Accessibility score | 75 | no change | no change |
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| Median axe violations / page | 5 | no change | no change |
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| Median page weight (KB) | 5182 KB | +192 KB worse | -176 KB better |
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| Reading ease (Flesch) | 44.2 | -1.7999999999999972 worse | +1.2000000000000028 better |
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| Standards checks passing (%) | 53% | no change | -4% worse |
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Accessible? — severity over time
Pages affected by axe severity over 17 weeks (lower is better)
Pages affected by axe severity, by week
| Week | Critical | Serious | Moderate | Minor |
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| 2026-W24 | 108 | 263 | 1513 | 12 |
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| 2026-W25 | 375 | 825 | 3083 | 42 |
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| 2026-W26 | 337 | 787 | 3003 | 50 |
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| 2026-W27 | 419 | 985 | 3147 | 71 |
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| 2026-W28 | 505 | 1091 | 3528 | 135 |
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| 2026-W29 | 823 | 1838 | 6052 | 230 |
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| 2026-W30 | 786 | 1785 | 5602 | 216 |
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| 2026-W31 | 855 | 1853 | 6057 | 252 |
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| 2026-W32 | 770 | 1792 | 5844 | 290 |
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| 2026-W33 | 726 | 1642 | 5774 | 250 |
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| 2026-W34 | 817 | 1863 | 5732 | 218 |
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| 2026-W35 | 468 | 1073 | 3259 | 135 |
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| 2026-W36 | 789 | 1811 | 5689 | 240 |
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| 2026-W37 | 718 | 1786 | 5611 | 218 |
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| 2026-W38 | 440 | 1020 | 3218 | 146 |
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| 2026-W39 | 759 | 1897 | 6493 | 251 |
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| 2026-W40 | 429 | 1119 | 3776 | 136 |
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Fast? — Lighthouse over time
Lighthouse category scores over 17 weeks
Lighthouse category scores by week
| Week | Performance | Accessibility | Best practices | SEO |
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| 2026-W24 | 82 | 100 | 100 | 100 |
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| 2026-W25 | 77 | 100 | 96 | 100 |
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| 2026-W26 | 78 | 100 | 96 | 100 |
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| 2026-W27 | 80 | 100 | 100 | 100 |
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| 2026-W28 | 82 | 100 | 96 | 100 |
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| 2026-W29 | 82 | 100 | 96 | 100 |
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| 2026-W30 | 84 | 100 | 96 | 100 |
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| 2026-W31 | 82 | 100 | 96 | 100 |
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| 2026-W32 | 82 | 100 | 96 | 100 |
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| 2026-W33 | 77 | 100 | 96 | 100 |
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| 2026-W34 | 79 | 100 | 96 | 100 |
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| 2026-W35 | 83 | 100 | 96 | 100 |
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| 2026-W36 | 86 | 100 | 96 | 100 |
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| 2026-W37 | 80 | 100 | 96 | 100 |
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| 2026-W38 | 83 | 100 | 96 | 100 |
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| 2026-W39 | 80 | 99 | 100 | 100 |
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| 2026-W40 | 82 | 100 | 100 | 100 |
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Lighthouse trend points are based on sampled pages and can vary week-to-week depending on which pages were sampled.
Sustainable? — page weight, requests & carbon over time
Median page weight (KB) over 17 weeks — better (5417 KB → 5182 KB)
Median page weight (KB) by week
| Week | Median page weight (KB) |
|---|
| 2026-W24 | 5417 KB |
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| 2026-W25 | 5379 KB |
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| 2026-W26 | 5288 KB |
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| 2026-W27 | 5358 KB |
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| 2026-W28 | 5247 KB |
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| 2026-W29 | 5266 KB |
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| 2026-W30 | 5119 KB |
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| 2026-W31 | 5196 KB |
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| 2026-W32 | 5114 KB |
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| 2026-W33 | 5149 KB |
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| 2026-W34 | 5034 KB |
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| 2026-W35 | 5149 KB |
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| 2026-W36 | 4990 KB |
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| 2026-W37 | 5278 KB |
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| 2026-W38 | 5155 KB |
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| 2026-W39 | 5099 KB |
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| 2026-W40 | 5182 KB |
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Median requests per page over 17 weeks — worse (44 → 47)
Median requests per page by week
| Week | Median requests per page |
|---|
| 2026-W24 | 44 |
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| 2026-W25 | 45 |
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| 2026-W26 | 45 |
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| 2026-W27 | 46 |
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| 2026-W28 | 45 |
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| 2026-W29 | 44 |
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| 2026-W30 | 44 |
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| 2026-W31 | 44 |
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| 2026-W32 | 44 |
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| 2026-W33 | 44 |
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| 2026-W34 | 44 |
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| 2026-W35 | 44 |
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| 2026-W36 | 44 |
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| 2026-W37 | 45 |
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| 2026-W38 | 45 |
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| 2026-W39 | 45 |
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| 2026-W40 | 47 |
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Mean CO₂ per page (g) over 17 weeks — better (1.042 g → 0.7787 g)
Mean CO₂ per page (g) by week
| Week | Mean CO₂ per page (g) |
|---|
| 2026-W24 | 1.042 g |
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| 2026-W25 | 0.9051 g |
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| 2026-W26 | 0.887 g |
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| 2026-W27 | 0.913 g |
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| 2026-W28 | 0.7214 g |
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| 2026-W29 | 0.8739 g |
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| 2026-W30 | 0.7495 g |
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| 2026-W31 | 0.7433 g |
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| 2026-W32 | 0.801 g |
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| 2026-W33 | 0.7794 g |
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| 2026-W34 | 0.6771 g |
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| 2026-W35 | 0.823 g |
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| 2026-W36 | 0.88 g |
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| 2026-W37 | 0.8498 g |
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| 2026-W38 | 0.8179 g |
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| 2026-W39 | 0.7096 g |
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| 2026-W40 | 0.7787 g |
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Findable? — readability over time
Reading ease (Flesch) over 17 weeks — better (43.1 → 44.2)
Reading ease (Flesch) by week
| Week | Reading ease (Flesch) |
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| 2026-W24 | 43.1 |
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| 2026-W25 | 43.9 |
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| 2026-W26 | 42 |
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| 2026-W27 | 43 |
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| 2026-W28 | 44.2 |
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| 2026-W29 | 45 |
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| 2026-W30 | 43.9 |
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| 2026-W31 | 44 |
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| 2026-W32 | 45.1 |
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| 2026-W33 | 44 |
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| 2026-W34 | 44.7 |
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| 2026-W35 | 46.3 |
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| 2026-W36 | 46 |
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| 2026-W37 | 44 |
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| 2026-W38 | 45 |
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| 2026-W39 | 46 |
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| 2026-W40 | 44.2 |
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Reading grade (Flesch-Kincaid) over 17 weeks — worse (12.3 → 12.5)
Reading grade (Flesch-Kincaid) by week
| Week | Reading grade (Flesch-Kincaid) |
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| 2026-W24 | 12.3 |
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| 2026-W25 | 12.5 |
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| 2026-W26 | 13 |
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| 2026-W27 | 13 |
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| 2026-W28 | 12.5 |
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| 2026-W29 | 13 |
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| 2026-W30 | 12.6 |
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| 2026-W31 | 12.5 |
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| 2026-W32 | 12.4 |
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| 2026-W33 | 12 |
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| 2026-W34 | 12.4 |
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| 2026-W35 | 12.1 |
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| 2026-W36 | 12 |
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| 2026-W37 | 12 |
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| 2026-W38 | 12 |
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| 2026-W39 | 12 |
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| 2026-W40 | 12.5 |
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Words per page (median) over 17 weeks — 624 → 707
Words per page (median) by week
| Week | Words per page (median) |
|---|
| 2026-W24 | 624 |
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| 2026-W25 | 819 |
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| 2026-W26 | 766 |
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| 2026-W27 | 763 |
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| 2026-W28 | 759 |
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| 2026-W29 | 745 |
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| 2026-W30 | 716 |
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| 2026-W31 | 730 |
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| 2026-W32 | 781 |
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| 2026-W33 | 726 |
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| 2026-W34 | 736 |
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| 2026-W35 | 777 |
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| 2026-W36 | 759 |
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| 2026-W37 | 737 |
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| 2026-W38 | 793 |
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| 2026-W39 | 716 |
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| 2026-W40 | 707 |
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Trustworthy? — technology & standards over time
Technologies detected over 16 weeks — 13 → 11
Technologies detected by week
| Week | Technologies detected |
|---|
| 2026-W25 | 13 |
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| 2026-W26 | 16 |
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| 2026-W27 | 14 |
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| 2026-W28 | 14 |
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| 2026-W29 | 22 |
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| 2026-W30 | 23 |
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| 2026-W31 | 18 |
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| 2026-W32 | 22 |
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| 2026-W33 | 19 |
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| 2026-W34 | 16 |
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| 2026-W35 | 22 |
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| 2026-W36 | 18 |
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| 2026-W37 | 18 |
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| 2026-W38 | 13 |
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| 2026-W39 | 23 |
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| 2026-W40 | 11 |
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Standards checks passing (%) over 16 weeks — worse (56% → 53%)
Standards checks passing (%) by week
| Week | Standards checks passing (%) |
|---|
| 2026-W25 | 56% |
|---|
| 2026-W26 | 59% |
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| 2026-W27 | 57% |
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| 2026-W28 | 55% |
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| 2026-W29 | 57% |
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| 2026-W30 | 53% |
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| 2026-W31 | 53% |
|---|
| 2026-W32 | 53% |
|---|
| 2026-W33 | 55% |
|---|
| 2026-W34 | 51% |
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| 2026-W35 | 52% |
|---|
| 2026-W36 | 53% |
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| 2026-W37 | 54% |
|---|
| 2026-W38 | 53% |
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| 2026-W39 | 52% |
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| 2026-W40 | 53% |
|---|
Security checks passing (%) over 16 weeks — unchanged
Security checks passing (%) by week
| Week | Security checks passing (%) |
|---|
| 2026-W25 | 50% |
|---|
| 2026-W26 | 50% |
|---|
| 2026-W27 | 50% |
|---|
| 2026-W28 | 50% |
|---|
| 2026-W29 | 50% |
|---|
| 2026-W30 | 50% |
|---|
| 2026-W31 | 50% |
|---|
| 2026-W32 | 50% |
|---|
| 2026-W33 | 50% |
|---|
| 2026-W34 | 50% |
|---|
| 2026-W35 | 50% |
|---|
| 2026-W36 | 50% |
|---|
| 2026-W37 | 50% |
|---|
| 2026-W38 | 50% |
|---|
| 2026-W39 | 50% |
|---|
| 2026-W40 | 50% |
|---|