---
title: "Split-half reliability (Spearman-Brown corrected)"
method_id: SM.RLB.INT.SCALE.SPLITHALF
family: Reliability
version: 1.1.0
date_modified: 2026-06-18
canonical: https://clarus.ofrencber.com/library/split_half_reliability.md
source: Clarus method library
---

# Split-half reliability (Spearman-Brown corrected)

> A classical statistical method in the Clarus library (Reliability family).
> Clarus selects, assumption-checks and runs this method on your data with a
> deterministic rule engine and real numerical libraries (scipy / statsmodels);
> it never generates numbers, citations or results.

**Also known as:** split-half coefficient; Spearman-Brown split-half reliability; split-half method; stepped-up half-test correlation.

## Hypotheses

- **Null (H0):** not_applicable
- **Alternative (H1):** not_applicable

## When to use it

Use this method when your goal is to:
- assess internal consistency reliability
- summarise a multi item scale
- report reliability of a summed or averaged score

## Data it expects

- **dependent:** not_applicable (no single outcome — a set of items measured on the same scale)
- **independent:** not_applicable
- **items:** >=4 numeric items on a common scale (Likert/interval), all keyed in the same direction, splittable into two comparable halves
- **pairing:** each case answers every item (wide person x item matrix)

## Assumptions Clarus checks

- **equal half length and variance** (severity: warning; on violation: warn_only)
- **split dependence** (severity: warning; on violation: warn_only)
- **unidimensionality** (severity: warning; on violation: warn_only)

## Effect size reported

- **r sb** (Spearman (1910); Brown (1910))

## Honest limitations

- The split-half coefficient depends on WHICH split is used; the conventional odd-even split is arbitrary, and a different partition would give a different number.
- The Spearman-Brown step-up assumes the two halves are parallel (equal length and variance); with an odd item count or unequal halves it is approximate.
- Cronbach's alpha equals the mean of all possible split-half coefficients and removes the split dependence — prefer it when split choice could be disputed.
- A negative half-half correlation almost always means some items are reverse-keyed and were not recoded.
- The coefficient is sample-dependent: it describes consistency in THIS sample and generalizes only to similar populations and conditions.

## Primary sources

- Spearman, C. (1910). Correlation calculated from faulty data. British Journal of Psychology, 3(3), 271-295. https://doi.org/10.1111/j.2044-8295.1910.tb00206.x
- Brown, W. (1910). Some experimental results in the correlation of mental abilities. British Journal of Psychology, 3(3), 296-322. https://doi.org/10.1111/j.2044-8295.1910.tb00207.x
- Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometrika, 16(3), 297-334. https://doi.org/10.1007/BF02310555
- Cortina, J. M. (1993). What is coefficient alpha? An examination of theory and applications. Journal of Applied Psychology, 78(1), 98-104. https://doi.org/10.1037/0021-9010.78.1.98
- George, D., & Mallery, P. (2003). SPSS for Windows Step by Step (4th ed.). Allyn & Bacon — reliability magnitude rule-of-thumb bands.
- Field, A. (2013). Discovering Statistics Using IBM SPSS Statistics (4th ed.), Ch.17.

## How to cite this

To cite this Clarus method page (the page itself — for the method's own primary sources, see above):

**Plain text**

Clarus, "Split-half reliability (Spearman-Brown corrected)", version 1.1.0, Clarus method library, 2026. https://clarus.ofrencber.com/library/split_half_reliability.md

**APA**

Clarus. (2026). Split-half reliability (Spearman-Brown corrected) (Version 1.1.0) [Statistical method, Clarus method library]. Retrieved from https://clarus.ofrencber.com/library/split_half_reliability.md

**BibTeX**

```bibtex
@misc{clarus-split-half-reliability,
  author       = {Clarus},
  title        = {Split-half reliability (Spearman-Brown corrected)},
  howpublished = {Clarus method library},
  version      = {1.1.0},
  year         = {2026},
  url          = {https://clarus.ofrencber.com/library/split_half_reliability.md}
}
```

_No DOI is minted for Clarus method pages yet; this citation uses the canonical URL, version and date. Cite the primary sources above for the method's scientific provenance._

---

METHOD SM.RLB.INT.SCALE.SPLITHALF · VERSION 1.1.0 · UPDATED 2026-06-18 · SOURCE Clarus method library