Split-Half Reliability

Split-half reliability is a statistical measure that assesses the internal consistency, or reliability, of a psychometric test or questionnaire. It evaluates whether the items within a test are consistently measuring the same construct by splitting the test into two halves.

How Split-Half Reliability is Measured

To measure split-half reliability, the test is divided into two halves, typically by splitting it down the middle. Each half should contain a representative sample of items, covering the entire range of the construct being measured. The scores from each half are then compared to examine the consistency between the two halves.

Methods of Splitting the Test

Several methods can be used to split the test into two halves:

  • Odd-Even Split: Items with odd numbers are placed in one half, while items with even numbers are placed in the other half.
  • Random Split: Items are randomly assigned to each half.
  • Equivalent-Form Split: Two different forms of the test are created, with each form containing similar items but in a different order.

Calculating Split-Half Reliability

The most commonly used method to calculate split-half reliability is Spearman-Brown prophecy formula, which adjusts the observed split-half correlation coefficient to estimate the reliability of the full-length test. Other methods, such as the Kuder-Richardson formula, can also be used depending on the type of data and test structure.

Interpreting the Results

Split-half reliability is represented by a correlation coefficient that ranges between 0 and 1. A higher correlation coefficient indicates greater internal consistency and higher reliability. A commonly accepted threshold for acceptable split-half reliability is a coefficient of 0.70 or above, although this may vary depending on the context and purpose of the test. Additionally, it is essential to consider the specific construct being measured and the characteristics of the sample used.

Limitations of Split-Half Reliability

While split-half reliability provides valuable insight into the internal consistency of a test, it has some limitations:

  • Length Effects: Longer tests often result in higher split-half reliability coefficients due to the wider range of items assessed.
  • Order Effects: For tests relying on equivalent-form splits, the order in which the items are presented can influence the results.
  • Homogeneity Assumption: Split-half reliability assumes that the construct being measured is homogeneous and does not account for potential subgroups within the test items.

Despite these limitations, split-half reliability remains a widely used and valuable method for assessing the internal consistency of psychometric tests and questionnaires.