{
  "title": "Scale reliability checker",
  "human_url": "https://happytails.ai/en/calculators/scale-reliability-checker/",
  "agent_url": "https://happytails.ai/agents/en/calculators/scale-reliability-checker/",
  "language": "en",
  "markdown_url": "https://happytails.ai/en/calculators/scale-reliability-checker.md",
  "content": "Scale reliability checker\nCheck the internal consistency of a questionnaire scale with Cronbach's alpha, its confidence interval, alpha if each item is deleted and corrected item-total correlations. Reverse-worded items are recoded before analysis.\nHow can we improve this tool?\nReport a problem or share an idea.\nPlease leave out private information. Your message and the tool name go to our team via PostHog.\nHow to use Scale reliability checker\nPaste CSV with one column per item and one row per respondent.\nList any reverse-worded items (none are reversed by default) and give the scale minimum and maximum.\nChoose how blank cells are handled and the confidence level.\nCalculate, review weak items, and download the report and CSV tables.\nUseful next steps\nCorrelation comparison\nAgreement analysis\nStandard deviation\nBox plot comparison\nWhat alpha measures\nCronbach's alpha (Cronbach 1951, Psychometrika 16:297) compares the sum of item variances with the variance of the total score. The interval uses Feldt's F-distribution method (Feldt 1965, Psychometrika 30:357). Standardized alpha uses the mean inter-item correlation. Alpha if item deleted and the corrected item-total correlation (each item against the total of the other items) show which items fit the scale least.\nReverse coding\nA reverse-worded item is recoded as minimum plus maximum minus the score before anything is computed. Forgetting this step can make alpha small or negative, so check the item-total correlations for negative values.\nAssumptions and limits\nAlpha assumes the items measure one construct with similar loadings. It is not evidence of validity, and a high value can come from many similar items. Blank cells either stop the analysis or drop the whole respondent.",
  "content_format": "text/plain",
  "visibility": "public",
  "links": [
    {
      "name": "Correlation comparison",
      "url": "https://happytails.ai/en/calculators/correlation-comparison/"
    },
    {
      "name": "Agreement analysis",
      "url": "https://happytails.ai/en/calculators/agreement-analysis/"
    },
    {
      "name": "Standard deviation",
      "url": "https://happytails.ai/en/calculators/standard-deviation/"
    },
    {
      "name": "Box plot comparison",
      "url": "https://happytails.ai/en/calculators/box-plot-comparison/"
    }
  ],
  "tool": {
    "id": "scale-reliability-checker",
    "category": "calculators",
    "built": true,
    "requirements": "Runs locally in your browser; nothing is uploaded. Paste up to 1,000,000 characters of CSV with at most 100 columns in total (including any ID column), 2 to 100 item columns, 3 to 10,000 respondents and at most 50,000 item scores in total. Blank lines at the end are ignored. Scores are plain numbers inside the declared minimum and maximum. Downloads: a JSON report plus CSV item statistics and an inter-item correlation matrix.",
    "implementation": {
      "fields": [
        {
          "key": "itemColumns",
          "label": "Item columns (optional)",
          "value": "",
          "type": "text",
          "maxLength": 20000,
          "help": "Comma-separated exact headers. Leave blank to use every column. The CSV may have at most 100 columns in total."
        },
        {
          "key": "reverseItems",
          "label": "Reverse-coded items (optional)",
          "value": "",
          "type": "text",
          "maxLength": 20000,
          "help": "Comma-separated exact headers of negatively worded items, for example q4. Leave blank when no item is reverse-worded. Requires the scale minimum and maximum."
        },
        {
          "key": "scaleMin",
          "label": "Scale minimum",
          "value": "1",
          "type": "text",
          "maxLength": 40,
          "help": "Lowest possible score, for example 1. Every score must lie inside the range."
        },
        {
          "key": "scaleMax",
          "label": "Scale maximum",
          "value": "5",
          "type": "text",
          "maxLength": 40,
          "help": "Highest possible score, for example 5."
        },
        {
          "key": "missing",
          "label": "Blank cells",
          "value": "reject",
          "type": "select",
          "values": [
            "reject",
            "drop"
          ],
          "labels": {
            "reject": "Stop and show an error",
            "drop": "Drop incomplete respondents"
          }
        },
        {
          "key": "confidence",
          "label": "Confidence level",
          "value": "0.95",
          "type": "text",
          "maxLength": 40,
          "help": "A proportion from 0.5 to 0.9999, for example 0.95."
        }
      ],
      "registrationFamily": "statistical-analysis-reference",
      "inputMaxLength": 1000000,
      "inputErrorCode": "STATISTICAL_ANALYSIS_REFERENCE_TOO_LONG",
      "note": "Runs on your device. Paste up to 1,000,000 characters of CSV with one column per item: 2 to 100 items in at most 100 columns, up to 10,000 respondents and 50,000 scores in total.",
      "experience": {
        "automatic": false,
        "single": false,
        "inputMaxLength": 1000000,
        "inputMode": "text",
        "label": "Item scores CSV",
        "placeholder": "q1,q2,q3\n4,5,3",
        "help": "One header row of item names, then one row per respondent with numeric scores. Up to 1,000,000 characters. Review the settings before running.",
        "action": null
      },
      "mode": "explicit",
      "interactive": false
    },
    "execution": "Browser interface",
    "api": null,
    "browser_agent": {
      "supported": true,
      "name": "run_current_tool",
      "discovery": "WebMCP on the human page in a supporting browser",
      "verification": "See audit/API-AUDIT.md; availability is not verification"
    }
  },
  "markdown": "# Scale reliability checker\n\n- Human page: https://happytails.ai/en/calculators/scale-reliability-checker/\n- Markdown: https://happytails.ai/en/calculators/scale-reliability-checker.md\n- Structured JSON: https://happytails.ai/agents/en/calculators/scale-reliability-checker/index.json\n- Visibility: public\n\n## Tool capabilities\n\n| Property | Value |\n| --- | --- |\n| Tool ID | `scale-reliability-checker` |\n| Category | calculators |\n| Implementation | Registered implementation. Registration alone is not a production-quality guarantee. |\n| Browser execution | Use the visible action or interactive controls. |\n| Browser processing | Browser; see tool notes for network behavior. |\n| HTTP API | Not callable through HTTP. |\n| Browser-agent interface | run_current_tool |\n\n### Implementation notes\n\nRuns on your device. Paste up to 1,000,000 characters of CSV with one column per item: 2 to 100 items in at most 100 columns, up to 10,000 respondents and 50,000 scores in total.\n\n### Inputs and settings\n\nText input: Item scores CSV.\n\nExample or placeholder shown in the interface (not a validated fixture):\n\n```text\nq1,q2,q3\n4,5,3\n```\n\nOne header row of item names, then one row per respondent with numeric scores. Up to 1,000,000 characters. Review the settings before running.\n\n| Setting | Meaning | Control type | Default | Constraints |\n| --- | --- | --- | --- | --- |\n| `itemColumns` | Item columns (optional) | text | \"\" |  |\n| `reverseItems` | Reverse-coded items (optional) | text | \"\" |  |\n| `scaleMin` | Scale minimum | text | \"1\" |  |\n| `scaleMax` | Scale maximum | text | \"5\" |  |\n| `missing` | Blank cells | select | \"reject\" | Allowed: reject, drop |\n| `confidence` | Confidence level | text | \"0.95\" |  |\n\n### Browser-agent workflow\n\n1. Open the human page in a browser that supports WebMCP.\n2. Discover the interface exposed by that page; use its actual schema.\n3. Select files on the page first when the tool requires files.\n4. Call `run_current_tool` with valid input and settings.\n5. Inspect the returned result or error and the displayed output. Retrieve files from the displayed download links.\n\nCalls do not automatically copy or download results. Browser permissions still apply. Interface availability alone is not proof of successful execution.\n\n### Planning specification\n\nRuns locally in your browser; nothing is uploaded. Paste up to 1,000,000 characters of CSV with at most 100 columns in total (including any ID column), 2 to 100 item columns, 3 to 10,000 respondents and at most 50,000 item scores in total. Blank lines at the end are ignored. Scores are plain numbers inside the declared minimum and maximum. Downloads: a JSON report plus CSV item statistics and an inter-item correlation matrix.\n\nThis describes intended requirements. Use the implementation notes, interface schema and observed output to determine current support.\n\n### Complete machine-readable capability record\n\n```json\n{\n  \"id\": \"scale-reliability-checker\",\n  \"category\": \"calculators\",\n  \"built\": true,\n  \"requirements\": \"Runs locally in your browser; nothing is uploaded. Paste up to 1,000,000 characters of CSV with at most 100 columns in total (including any ID column), 2 to 100 item columns, 3 to 10,000 respondents and at most 50,000 item scores in total. Blank lines at the end are ignored. Scores are plain numbers inside the declared minimum and maximum. Downloads: a JSON report plus CSV item statistics and an inter-item correlation matrix.\",\n  \"implementation\": {\n    \"fields\": [\n      {\n        \"key\": \"itemColumns\",\n        \"label\": \"Item columns (optional)\",\n        \"value\": \"\",\n        \"type\": \"text\",\n        \"maxLength\": 20000,\n        \"help\": \"Comma-separated exact headers. Leave blank to use every column. The CSV may have at most 100 columns in total.\"\n      },\n      {\n        \"key\": \"reverseItems\",\n        \"label\": \"Reverse-coded items (optional)\",\n        \"value\": \"\",\n        \"type\": \"text\",\n        \"maxLength\": 20000,\n        \"help\": \"Comma-separated exact headers of negatively worded items, for example q4. Leave blank when no item is reverse-worded. Requires the scale minimum and maximum.\"\n      },\n      {\n        \"key\": \"scaleMin\",\n        \"label\": \"Scale minimum\",\n        \"value\": \"1\",\n        \"type\": \"text\",\n        \"maxLength\": 40,\n        \"help\": \"Lowest possible score, for example 1. Every score must lie inside the range.\"\n      },\n      {\n        \"key\": \"scaleMax\",\n        \"label\": \"Scale maximum\",\n        \"value\": \"5\",\n        \"type\": \"text\",\n        \"maxLength\": 40,\n        \"help\": \"Highest possible score, for example 5.\"\n      },\n      {\n        \"key\": \"missing\",\n        \"label\": \"Blank cells\",\n        \"value\": \"reject\",\n        \"type\": \"select\",\n        \"values\": [\n          \"reject\",\n          \"drop\"\n        ],\n        \"labels\": {\n          \"reject\": \"Stop and show an error\",\n          \"drop\": \"Drop incomplete respondents\"\n        }\n      },\n      {\n        \"key\": \"confidence\",\n        \"label\": \"Confidence level\",\n        \"value\": \"0.95\",\n        \"type\": \"text\",\n        \"maxLength\": 40,\n        \"help\": \"A proportion from 0.5 to 0.9999, for example 0.95.\"\n      }\n    ],\n    \"registrationFamily\": \"statistical-analysis-reference\",\n    \"inputMaxLength\": 1000000,\n    \"inputErrorCode\": \"STATISTICAL_ANALYSIS_REFERENCE_TOO_LONG\",\n    \"note\": \"Runs on your device. Paste up to 1,000,000 characters of CSV with one column per item: 2 to 100 items in at most 100 columns, up to 10,000 respondents and 50,000 scores in total.\",\n    \"experience\": {\n      \"automatic\": false,\n      \"single\": false,\n      \"inputMaxLength\": 1000000,\n      \"inputMode\": \"text\",\n      \"label\": \"Item scores CSV\",\n      \"placeholder\": \"q1,q2,q3\\n4,5,3\",\n      \"help\": \"One header row of item names, then one row per respondent with numeric scores. Up to 1,000,000 characters. Review the settings before running.\",\n      \"action\": null\n    },\n    \"mode\": \"explicit\",\n    \"interactive\": false\n  },\n  \"execution\": \"Browser interface\",\n  \"api\": null,\n  \"browser_agent\": {\n    \"supported\": true,\n    \"name\": \"run_current_tool\",\n    \"discovery\": \"WebMCP on the human page in a supporting browser\",\n    \"verification\": \"See audit/API-AUDIT.md; availability is not verification\"\n  }\n}\n```\n\n## Page guide\n\nCheck the internal consistency of a questionnaire scale with Cronbach's alpha, its confidence interval, alpha if each item is deleted and corrected item-total correlations. Reverse-worded items are recoded before analysis.\n\nHow can we improve this tool?\n\nReport a problem or share an idea.\n\nPlease leave out private information. Your message and the tool name go to our team via PostHog.\n\n### How to use Scale reliability checker\n\n1. Paste CSV with one column per item and one row per respondent.\n2. List any reverse-worded items (none are reversed by default) and give the scale minimum and maximum.\n3. Choose how blank cells are handled and the confidence level.\n4. Calculate, review weak items, and download the report and CSV tables.\n\n## Useful next steps\n\n- [Correlation comparison](https://happytails.ai/en/calculators/correlation-comparison/) ([Markdown](https://happytails.ai/en/calculators/correlation-comparison.md))\n\n- [Agreement analysis](https://happytails.ai/en/calculators/agreement-analysis/) ([Markdown](https://happytails.ai/en/calculators/agreement-analysis.md))\n\n- [Standard deviation](https://happytails.ai/en/calculators/standard-deviation/) ([Markdown](https://happytails.ai/en/calculators/standard-deviation.md))\n\n- [Box plot comparison](https://happytails.ai/en/calculators/box-plot-comparison/) ([Markdown](https://happytails.ai/en/calculators/box-plot-comparison.md))\n\n## What alpha measures\n\nCronbach's alpha (Cronbach 1951, Psychometrika 16:297) compares the sum of item variances with the variance of the total score. The interval uses Feldt's F-distribution method (Feldt 1965, Psychometrika 30:357). Standardized alpha uses the mean inter-item correlation. Alpha if item deleted and the corrected item-total correlation (each item against the total of the other items) show which items fit the scale least.\n\n### Reverse coding\n\nA reverse-worded item is recoded as minimum plus maximum minus the score before anything is computed. Forgetting this step can make alpha small or negative, so check the item-total correlations for negative values.\n\n### Assumptions and limits\n\nAlpha assumes the items measure one construct with similar loadings. It is not evidence of validity, and a high value can come from many similar items. Blank cells either stop the analysis or drop the whole respondent.\n"
}