{
  "slug": "sampling-design",
  "term": "Sampling design",
  "aliases": [],
  "definition": "A sampling design specifies the possible samples from a population and the probability with which each sample is selected.",
  "note": "For storage verification, define the object version, sampling unit and selection rule: uniformly choosing C distinct blocks is different from choosing one contiguous C-block window with a random start. Uniform inclusion probability for each block alone does not make every size-C subset equally likely. [hesela-design]\n\nWith N fixed blocks and M fixed damaged positions, a uniform size-C subset has hit probability 1 - choose(N-M,C)/choose(N,C). This uses a hypergeometric model and does not require independent damage locations. Replacing the sampled set changes the design; sorting that same set changes only order under an unchanged object and completed verification. [nist-hypergeometric] [pdp2007] [hesela-design]\n\nHesela's cyclic example compares 460 checked blocks out of 10,000 with one constructed 100-block damaged run: uniform subsets detect it with about 99.12% probability, while one random-start window gives 5.59%. Both have expected damaged-block count 4.6. This is a counting example with perfect recognition, not measured HDD behavior or a scrub recommendation. [hesela-design]",
  "related": [
    "data-scrubbing",
    "provable-data-possession",
    "staggered-scrubbing",
    "backup-verification"
  ],
  "citations": [
    {
      "id": "nist-hypergeometric",
      "title": "NIST Dataplot Reference Manual: HYPCDF, finite-population sampling without replacement.",
      "url": "https://www.itl.nist.gov/div898/software/dataplot/refman2/ch8/hypcdf.pdf",
      "accessed": "2026-10-18"
    },
    {
      "id": "pdp2007",
      "title": "Ateniese et al. Provable Data Possession at Untrusted Stores. CCS 2007, section 5.1.",
      "url": "https://people.eecs.berkeley.edu/~dawnsong/papers/p598-ateniese",
      "accessed": "2026-10-18"
    },
    {
      "id": "hesela-design",
      "title": "Hesela: sampling-design counterexample, derivation and enumerated tests.",
      "url": "https://hesela.com/analyses/scrubbing-detection-not-durability/#sampling-design",
      "accessed": "2026-10-18"
    }
  ],
  "status": "research",
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-18"
}