{
  "schema_version": "1.0",
  "title": "AFR worked examples",
  "data_origin": "synthetic educational inputs, not observed drive data",
  "published_on": "2026-10-10",
  "method": {
    "days_per_year": 365,
    "confidence_level": 0.95,
    "interval": "Equal-tailed Garwood Poisson count interval scaled by 36500 / drive_days",
    "assumptions": "Poisson count model conditional on exposure; not a validation of fleet independence or stationarity.",
    "probability_conversion": "1 - exp(-annual_rate), only under a constant individual hazard"
  },
  "environment": {
    "python": "3.12.3",
    "numpy": "2.5.4",
    "scipy": "1.17.1"
  },
  "code_sha256": {
    "reliability_stats.py": "a062722c7d75b06af98e262e95eb3bb0f296188fd2aac1226589cf38cdbccb82",
    "build-afr-method-examples.py": "7983aada17c1054340b900f6eff31e4ac1bc41d3b3978311cb9e529f958b7173"
  },
  "examples": [
    {
      "label": "Zero events, short exposure",
      "failures": 0,
      "drive_days": 365,
      "afr_percent": 0.0,
      "afr_lower95_percent": 0.0,
      "afr_upper95_percent": 368.8879454113936
    },
    {
      "label": "Zero events, 100 times more exposure",
      "failures": 0,
      "drive_days": 36500,
      "afr_percent": 0.0,
      "afr_lower95_percent": 0.0,
      "afr_upper95_percent": 3.6888794541139363
    },
    {
      "label": "One event, sparse exposure",
      "failures": 1,
      "drive_days": 100,
      "afr_percent": 365.0,
      "afr_lower95_percent": 9.240999914265805,
      "afr_upper95_percent": 2033.6498376926977
    },
    {
      "label": "Large-count numerical regression",
      "failures": 1000,
      "drive_days": 36500000,
      "afr_percent": 1.0,
      "afr_lower95_percent": 0.9389730184076952,
      "afr_upper95_percent": 1.063952136016302
    }
  ],
  "constant_hazard_comparisons": [
    {
      "annual_rate_percent": 1,
      "one_year_probability_percent": 0.9950166250831947
    },
    {
      "annual_rate_percent": 10,
      "one_year_probability_percent": 9.516258196404042
    },
    {
      "annual_rate_percent": 100,
      "one_year_probability_percent": 63.212055882855765
    },
    {
      "annual_rate_percent": 365,
      "one_year_probability_percent": 97.40088712212447
    }
  ],
  "sources": [
    "https://www.itl.nist.gov/div898/handbook/apr/section4/apr451.htm",
    "https://www.itl.nist.gov/div898/handbook/apr/section1/apr161.htm",
    "https://www.backblaze.com/blog/10-stories-from-10-years-of-drive-stats-data/"
  ]
}