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        "wikipedia_people_count": { "value": 17, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=9th-century_BC_births&depth=10", "notes": "" },
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      "start_year": -800,
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        "wikipedia_people_count": { "value": 37, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=8th-century_BC_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 2000, "tier": "T3", "source": "https://inscriptions.packhum.org/", "notes": "Growing Greek inscriptions; Earliest Latin texts" },
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      "start_year": -700,
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      "span_years": 100,
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        "wikipedia_people_count": { "value": 49, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=7th-century_BC_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 3000, "tier": "T3", "source": "https://inscriptions.packhum.org/", "notes": "Growing Greek epigraphic corpus" },
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      "start_year": -600,
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      "span_years": 100,
      "metrics": {
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        "named_individuals": { "value": 114, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=6th-century_BC_births&depth=10", "notes": "" },
        "wikipedia_people_count": { "value": 114, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=6th-century_BC_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
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      "start_year": -500,
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      "span_years": 100,
      "metrics": {
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        "wikipedia_people_count": { "value": 150, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=5th-century_BC_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
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      "start_year": -400,
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      "span_years": 100,
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        "wikipedia_people_count": { "value": 221, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=4th-century_BC_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
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      "start_year": -300,
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      "span_years": 100,
      "metrics": {
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        "named_individuals": { "value": 194, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=3rd-century_BC_births&depth=10", "notes": "" },
        "wikipedia_people_count": { "value": 194, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=3rd-century_BC_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 15000, "tier": "T3", "source": "https://inscriptions.packhum.org/", "notes": "Hellenistic Greek inscriptions; growing Latin" },
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      "start_year": -200,
      "end_year": -100,
      "span_years": 100,
      "metrics": {
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        "named_individuals": { "value": 260, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=2nd-century_BC_births&depth=10", "notes": "" },
        "wikipedia_people_count": { "value": 260, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=2nd-century_BC_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
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        "films_set_in_period": { "value": 4, "tier": "T1", "source": "https://en.wikipedia.org/w/api.php?action=query&prop=categoryinfo&titles=Category:Films_set_in_the_2nd_century_BC", "notes": "" }
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        "wikipedia_people_count": { "value": 355, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=1st-century_BC_births&depth=10", "notes": "" },
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        "wikipedia_people_count": { "value": 294, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=1st-century_births&depth=10", "notes": "" },
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      "start_year": 100,
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      "span_years": 100,
      "metrics": {
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        "wikipedia_events_count": null,
        "source_proxy": { "value": 40000, "tier": "T3", "source": "https://edh.ub.uni-heidelberg.de/home", "notes": "Peak Roman epigraphy (1st-3rd c. CE is the bulk of EDH)" },
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        "wikipedia_people_count": { "value": 493, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=3rd-century_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 35000, "tier": "T3", "source": "https://edh.ub.uni-heidelberg.de/home", "notes": "Roman epigraphy declining from 2nd c. peak" },
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      "span_years": 100,
      "metrics": {
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        "wikipedia_people_count": { "value": 467, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=4th-century_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
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      "start_year": 400,
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      "start_year": 500,
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      "metrics": {
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      "span_years": 100,
      "metrics": {
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        "wikipedia_people_count": { "value": 819, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=7th-century_births&depth=10", "notes": "" },
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    },
    {
      "label": "8th century",
      "start_year": 700,
      "end_year": 800,
      "span_years": 100,
      "metrics": {
        "openalex_work_count": { "value": 7880, "tier": "T1", "source": "https://api.openalex.org/works?search=%228th+century%22&filter=concepts.id:C95457728", "notes": "" },
        "named_individuals": { "value": 944, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=8th-century_births&depth=10", "notes": "" },
        "wikipedia_people_count": { "value": 944, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=8th-century_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 43703, "tier": "T2", "source": "https://api.ourworldindata.org/v1/indicators/1207432.data.json", "notes": "Carolingian renaissance begins" },
        "ngram_discourse": { "value": 1.201e-06, "tier": "T1", "source": "https://books.google.com/ngrams/", "notes": "Combined" },
        "films_set_in_period": { "value": 19, "tier": "T1", "source": "https://en.wikipedia.org/w/api.php?action=query&prop=categoryinfo&titles=Category:Films_set_in_the_8th_century", "notes": "" }
      }
    },
    {
      "label": "9th century",
      "start_year": 800,
      "end_year": 900,
      "span_years": 100,
      "metrics": {
        "openalex_work_count": { "value": 8400, "tier": "T1", "source": "https://api.openalex.org/works?search=%229th+century%22&filter=concepts.id:C95457728", "notes": "" },
        "named_individuals": { "value": 1251, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=9th-century_births&depth=10", "notes": "" },
        "wikipedia_people_count": { "value": 1251, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=9th-century_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 201742, "tier": "T2", "source": "https://api.ourworldindata.org/v1/indicators/1207432.data.json", "notes": "Carolingian peak" },
        "ngram_discourse": { "value": 1.187e-06, "tier": "T1", "source": "https://books.google.com/ngrams/", "notes": "Combined" },
        "films_set_in_period": { "value": 16, "tier": "T1", "source": "https://en.wikipedia.org/w/api.php?action=query&prop=categoryinfo&titles=Category:Films_set_in_the_9th_century", "notes": "" }
      }
    },
    {
      "label": "10th century",
      "start_year": 900,
      "end_year": 1000,
      "span_years": 100,
      "metrics": {
        "openalex_work_count": { "value": 9516, "tier": "T1", "source": "https://api.openalex.org/works?search=%2210th+century%22&filter=concepts.id:C95457728", "notes": "" },
        "named_individuals": { "value": 1311, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=10th-century_births&depth=10", "notes": "" },
        "wikipedia_people_count": { "value": 1311, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=10th-century_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 135638, "tier": "T2", "source": "https://api.ourworldindata.org/v1/indicators/1207432.data.json", "notes": "Post-Carolingian dip" },
        "ngram_discourse": { "value": 1.013e-06, "tier": "T1", "source": "https://books.google.com/ngrams/", "notes": "Combined; discourse trough for CE centuries" },
        "films_set_in_period": { "value": 28, "tier": "T1", "source": "https://en.wikipedia.org/w/api.php?action=query&prop=categoryinfo&titles=Category:Films_set_in_the_10th_century", "notes": "" }
      }
    },
    {
      "label": "11th century",
      "start_year": 1000,
      "end_year": 1100,
      "span_years": 100,
      "metrics": {
        "openalex_work_count": { "value": 10644, "tier": "T1", "source": "https://api.openalex.org/works?search=%2211th+century%22&filter=concepts.id:C95457728", "notes": "" },
        "named_individuals": { "value": 1797, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=11th-century_births&depth=10", "notes": "" },
        "wikipedia_people_count": { "value": 1797, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=11th-century_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 212029, "tier": "T2", "source": "https://api.ourworldindata.org/v1/indicators/1207432.data.json", "notes": "Medieval recovery" },
        "ngram_discourse": { "value": 1.174e-06, "tier": "T1", "source": "https://books.google.com/ngrams/", "notes": "Combined" },
        "films_set_in_period": { "value": 46, "tier": "T1", "source": "https://en.wikipedia.org/w/api.php?action=query&prop=categoryinfo&titles=Category:Films_set_in_the_11th_century", "notes": "" }
      }
    },
    {
      "label": "12th century",
      "start_year": 1100,
      "end_year": 1200,
      "span_years": 100,
      "metrics": {
        "openalex_work_count": { "value": 14242, "tier": "T1", "source": "https://api.openalex.org/works?search=%2212th+century%22&filter=concepts.id:C95457728", "notes": "" },
        "named_individuals": { "value": 2655, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=12th-century_births&depth=10", "notes": "" },
        "wikipedia_people_count": { "value": 2655, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=12th-century_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 768721, "tier": "T2", "source": "https://api.ourworldindata.org/v1/indicators/1207432.data.json", "notes": "12th-century renaissance" },
        "ngram_discourse": { "value": 1.974e-06, "tier": "T1", "source": "https://books.google.com/ngrams/", "notes": "Combined" },
        "films_set_in_period": { "value": 58, "tier": "T1", "source": "https://en.wikipedia.org/w/api.php?action=query&prop=categoryinfo&titles=Category:Films_set_in_the_12th_century", "notes": "" }
      }
    },
    {
      "label": "13th century",
      "start_year": 1200,
      "end_year": 1300,
      "span_years": 100,
      "metrics": {
        "openalex_work_count": { "value": 19025, "tier": "T1", "source": "https://api.openalex.org/works?search=%2213th+century%22&filter=concepts.id:C95457728", "notes": "" },
        "named_individuals": { "value": 3439, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=13th-century_births&depth=10", "notes": "" },
        "wikipedia_people_count": { "value": 3439, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=13th-century_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 1761952, "tier": "T2", "source": "https://api.ourworldindata.org/v1/indicators/1207432.data.json", "notes": "University system expansion" },
        "ngram_discourse": { "value": 2.318e-06, "tier": "T1", "source": "https://books.google.com/ngrams/", "notes": "Combined" },
        "films_set_in_period": { "value": 87, "tier": "T1", "source": "https://en.wikipedia.org/w/api.php?action=query&prop=categoryinfo&titles=Category:Films_set_in_the_13th_century", "notes": "" }
      }
    },
    {
      "label": "14th century",
      "start_year": 1300,
      "end_year": 1400,
      "span_years": 100,
      "metrics": {
        "openalex_work_count": { "value": 18545, "tier": "T1", "source": "https://api.openalex.org/works?search=%2214th+century%22&filter=concepts.id:C95457728", "notes": "" },
        "named_individuals": { "value": 4675, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=14th-century_births&depth=10", "notes": "" },
        "wikipedia_people_count": { "value": 4675, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=14th-century_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 2746951, "tier": "T2", "source": "https://api.ourworldindata.org/v1/indicators/1207432.data.json", "notes": "Late medieval peak" },
        "ngram_discourse": { "value": 2.114e-06, "tier": "T1", "source": "https://books.google.com/ngrams/", "notes": "Combined" },
        "films_set_in_period": { "value": 70, "tier": "T1", "source": "https://en.wikipedia.org/w/api.php?action=query&prop=categoryinfo&titles=Category:Films_set_in_the_14th_century", "notes": "" }
      }
    },
    {
      "label": "15th century",
      "start_year": 1400,
      "end_year": 1500,
      "span_years": 100,
      "metrics": {
        "openalex_work_count": { "value": 22839, "tier": "T1", "source": "https://api.openalex.org/works?search=%2215th+century%22&filter=concepts.id:C95457728", "notes": "" },
        "named_individuals": { "value": 7355, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=15th-century_births&depth=10", "notes": "" },
        "wikipedia_people_count": { "value": 7355, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=15th-century_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 4999160, "tier": "T2", "source": "https://api.ourworldindata.org/v1/indicators/1207432.data.json", "notes": "Pre-print peak + early incunabula (~27K editions)" },
        "ngram_discourse": { "value": 2.607e-06, "tier": "T1", "source": "https://books.google.com/ngrams/", "notes": "Combined" },
        "films_set_in_period": { "value": 95, "tier": "T1", "source": "https://en.wikipedia.org/w/api.php?action=query&prop=categoryinfo&titles=Category:Films_set_in_the_15th_century", "notes": "" }
      }
    },
    {
      "label": "16th century",
      "start_year": 1500,
      "end_year": 1600,
      "span_years": 100,
      "metrics": {
        "openalex_work_count": { "value": 36794, "tier": "T1", "source": "https://api.openalex.org/works?search=%2216th+century%22&filter=concepts.id:C95457728", "notes": "" },
        "named_individuals": { "value": 18250, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=16th-century_births&depth=10", "notes": "" },
        "wikipedia_people_count": { "value": 18250, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=16th-century_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 350000, "tier": "T1", "source": "https://en.wikipedia.org/wiki/Universal_Short_Title_Catalogue", "notes": "USTC: ~300-400K print titles; 200-400M copies" },
        "ngram_discourse": { "value": 4.827e-06, "tier": "T1", "source": "https://books.google.com/ngrams/", "notes": "Combined" },
        "films_set_in_period": { "value": 221, "tier": "T1", "source": "https://en.wikipedia.org/w/api.php?action=query&prop=categoryinfo&titles=Category:Films_set_in_the_16th_century", "notes": "" }
      }
    },
    {
      "label": "17th century",
      "start_year": 1600,
      "end_year": 1700,
      "span_years": 100,
      "metrics": {
        "openalex_work_count": { "value": 45472, "tier": "T1", "source": "https://api.openalex.org/works?search=%2217th+century%22&filter=concepts.id:C95457728", "notes": "" },
        "named_individuals": { "value": 25234, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=17th-century_births&depth=10", "notes": "" },
        "wikipedia_people_count": { "value": 25234, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=17th-century_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 700000, "tier": "T2", "source": "https://impact.wp.st-andrews.ac.uk/the-universal-short-title-catalogue/", "notes": "USTC projects ~1.4M editions 1450-1700; ~700K for 17th c. estimate" },
        "ngram_discourse": { "value": 5.875e-06, "tier": "T1", "source": "https://books.google.com/ngrams/", "notes": "Combined" },
        "films_set_in_period": { "value": 172, "tier": "T1", "source": "https://en.wikipedia.org/w/api.php?action=query&prop=categoryinfo&titles=Category:Films_set_in_the_17th_century", "notes": "" }
      }
    },
    {
      "label": "18th century",
      "start_year": 1700,
      "end_year": 1800,
      "span_years": 100,
      "metrics": {
        "openalex_work_count": { "value": 64527, "tier": "T1", "source": "https://api.openalex.org/works?search=%2218th+century%22&filter=concepts.id:C95457728", "notes": "" },
        "named_individuals": { "value": 61299, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=18th-century_births&depth=10", "notes": "" },
        "wikipedia_people_count": { "value": 61299, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=18th-century_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 2000000, "tier": "T2", "source": "https://www.britannica.com/topic/publishing/The-flourishing-book-trade-1550-1800", "notes": "Approaching 1 billion copies; ~2M titles estimated" },
        "ngram_discourse": { "value": 9.238e-06, "tier": "T1", "source": "https://books.google.com/ngrams/", "notes": "Combined" },
        "films_set_in_period": { "value": 331, "tier": "T1", "source": "https://en.wikipedia.org/w/api.php?action=query&prop=categoryinfo&titles=Category:Films_set_in_the_18th_century", "notes": "" }
      }
    },
    {
      "label": "19th century",
      "start_year": 1800,
      "end_year": 1900,
      "span_years": 100,
      "metrics": {
        "openalex_work_count": { "value": 138099, "tier": "T1", "source": "https://api.openalex.org/works?search=%2219th+century%22&filter=concepts.id:C95457728", "notes": "" },
        "named_individuals": { "value": 326525, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=19th-century_births&depth=10", "notes": "" },
        "wikipedia_people_count": { "value": 326525, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=19th-century_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 10000000, "tier": "T2", "source": "https://www.britannica.com/topic/publishing/Spread-of-education-and-literacy", "notes": "30K+ new titles/yr in Germany alone by 1910; mass literacy achieved" },
        "ngram_discourse": { "value": 2.082e-05, "tier": "T1", "source": "https://books.google.com/ngrams/", "notes": "Peak discourse century; combined" },
        "films_set_in_period": { "value": 905, "tier": "T1", "source": "https://en.wikipedia.org/w/api.php?action=query&prop=categoryinfo&titles=Category:Films_set_in_the_19th_century", "notes": "Most popular period for historical cinema" }
      }
    },
    {
      "label": "20th century",
      "start_year": 1900,
      "end_year": 2000,
      "span_years": 100,
      "metrics": {
        "openalex_work_count": { "value": 156016, "tier": "T1", "source": "https://api.openalex.org/works?search=%2220th+century%22&filter=concepts.id:C95457728", "notes": "" },
        "named_individuals": { "value": 1367010, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=20th-century_births&depth=10", "notes": "" },
        "wikipedia_people_count": { "value": 1367010, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=20th-century_births&depth=10", "notes": "" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 85000000, "tier": "T2", "source": "https://www.npr.org/2010/08/12/129160859/googles-tally-of-worlds-book-titles-129-864-880", "notes": "Google: ~130M unique books total by 2010; bulk from 20th c. Plus periodicals, film, audio" },
        "ngram_discourse": { "value": 2.000e-05, "tier": "T1", "source": "https://books.google.com/ngrams/", "notes": "Combined; slightly below 19th c." },
        "films_set_in_period": { "value": 181, "tier": "T1", "source": "https://en.wikipedia.org/w/api.php?action=query&prop=categoryinfo&titles=Category:Films_set_in_the_20th_century", "notes": "UNDERCOUNT: 20th c. films categorized by decade/conflict instead" }
      }
    },
    {
      "label": "21st century",
      "start_year": 2000,
      "end_year": 2100,
      "span_years": 100,
      "metrics": {
        "openalex_work_count": { "value": 82723, "tier": "T1", "source": "https://api.openalex.org/works?search=%2221st+century%22&filter=concepts.id:C95457728", "notes": "Inflated by non-historical forward-looking usage" },
        "named_individuals": { "value": 55394, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=21st-century_births&depth=10", "notes": "Partial century (2001-2026); many not yet notable" },
        "wikipedia_people_count": { "value": 55394, "tier": "T1", "source": "https://petscan.wmflabs.org/?categories=21st-century_births&depth=10", "notes": "Partial century" },
        "wikipedia_events_count": null,
        "source_proxy": { "value": 200000000, "tier": "T2", "source": "https://www.statista.com/statistics/871513/worldwide-data-created/", "notes": "Digital explosion: 64 ZB in 2020; ~2.2M new book titles/yr" },
        "ngram_discourse": { "value": 6.825e-06, "tier": "T1", "source": "https://books.google.com/ngrams/", "notes": "Combined; lower than expected as still 'present' not 'history'" },
        "films_set_in_period": { "value": 65, "tier": "T1", "source": "https://en.wikipedia.org/w/api.php?action=query&prop=categoryinfo&titles=Category:Films_set_in_the_21st_century", "notes": "Partial century" }
      }
    }
  ],
  "metadata": {
    "scope": "Anglophone/Western historical knowledge",
    "compiled_date": "2026-04-26",
    "collection_date": "2026-04-26",
    "collection_method": "Manual API queries and literature review",
    "api_versions": {"openalex": "2026-04", "petscan": "3.0", "google_ngrams": "en-2019"},
    "tier_definitions": {
      "T1": "Direct API query, fully reproducible",
      "T2": "Published research data, independently verifiable",
      "T3": "Manual estimate based on archaeological/bibliographic literature"
    },
    "excluded_metrics": {
      "wikipedia_people_count": "Identical to named_individuals (same PetScan source)",
      "wikipedia_events_count": "All null (Wikipedia category structure not as expected)",
      "films_set_in_period": "Supplementary only, excluded from composite"
    },
    "license": "CC-BY-4.0",
    "source_proxy_note": "Source proxy uses era-specific measures: inscriptions and archaeological tablets (antiquity), manuscript production estimates from Buringh & Van Zanden 2009 (medieval), print edition counts from USTC/Britannica (early modern), publication volume estimates (modern). Cross-era comparison is approximate.",
    "data_sources": [
      "OpenAlex API (academic works, History concept C95457728)",
      "PetScan / Wikipedia API (biography article counts)",
      "Google Books Ngram Viewer (discourse frequency 2000-2019, en-2019 corpus)",
      "Buringh & Van Zanden 2009 via Our World in Data (manuscript production)",
      "USTC / ISTC (print edition counts)",
      "Britannica / UNESCO (modern publication volumes)",
      "EDH / PHI / CDLI (inscription/tablet databases)",
      "Wikipedia Films categories (supplementary)"
    ],
    "known_limitations": [
      "Source proxy changes measure by era (inscriptions → manuscripts → print → publications)",
      "Wikipedia category sparsity before ~8th c. BC means some metrics are near-zero",
      "Ngram data measures contemporary discourse frequency, not knowledge itself",
      "Scope is Anglophone/Western; Chinese, Islamic, Indian historiographies would show different curves",
      "OpenAlex concept tagging may not perfectly map to centuries",
      "1st century CE ngram value inflated by non-historical 'first century' usage",
      "21st century metrics inflated by non-historical forward-looking usage",
      "Wikipedia events categories do not exist in expected format"
    ]
  }
}