Power & sample size API

Solves the power equation for two-means (Cohen's d) or two-proportions (Cohen's h): give n to get power, or give target power to get required n per group. Answers 'How many subjects per group do I need?', 'What is my statistical power at this sample size?'.

Price$0.08per request

MethodPOST

Route/v1/stats/power-analysis

StatusLive

MIME typeapplication/json

Rate limit120/minute

Cache0s public

statisticspowersample-sizeeffect-sizecohens-dexperiment-designplanninginference

API URLhttps://x402.hexl.dev/v1/stats/power-analysis

Integration docs

Example request

{
  "test": "two-means",
  "effectSize": 0.5,
  "power": 0.8
}

Example response

{
  "mode": "n-from-power",
  "test": "two-means",
  "effectSize": 0.5,
  "power": 0.8,
  "alpha": 0.05,
  "tail": "two",
  "nPerGroup": 63,
  "totalN": 126,
  "zAlpha": 1.96,
  "zBeta": 0.8416,
  "rating": "small study",
  "interpretation": "Need n=63/group (total 126) to detect effect 0.5 with 80% power at alpha=0.05."
}

Input schema

{
  "type": "object",
  "required": [],
  "properties": {
    "test": {
      "type": "string",
      "enum": [
        "two-means",
        "two-proportions"
      ]
    },
    "effectSize": {
      "type": "number",
      "examples": [
        0.5
      ]
    },
    "p1": {
      "type": "number"
    },
    "p2": {
      "type": "number"
    },
    "n": {
      "type": "integer"
    },
    "power": {
      "type": "number",
      "examples": [
        0.8
      ]
    },
    "alpha": {
      "type": "number",
      "examples": [
        0.05
      ]
    },
    "tail": {
      "type": "string",
      "enum": [
        "two",
        "one"
      ]
    }
  }
}

Output schema

{
  "type": "object",
  "additionalProperties": true
}