There are several reasons why inter-rater reliability may be low:

  1. Lack of clarity or ambiguity in the criteria: If the criteria used to evaluate the phenomenon are unclear or ambiguous, raters may have different interpretations and produce inconsistent ratings.

  2. Differences in judgment or perception: Raters may have different judgments or perceptions of the phenomenon being evaluated, which can lead to disagreements and inconsistent ratings.

  3. Rater bias: Raters may have personal biases or preferences that influence their evaluations, leading to inconsistent ratings.

  4. Inadequate training or lack of experience: If the raters are not adequately trained or do not have a clear understanding of the protocol or criteria, they may produce inconsistent ratings.

  5. Complexity of the phenomenon: If the phenomenon being evaluated is complex or difficult to evaluate, raters may have difficulty producing consistent ratings.

  6. Insufficient sample size: If the sample size is too small, it may be difficult to establish inter-rater reliability due to limited data.

By identifying the reasons for low inter-rater reliability, steps can be taken to address them and improve the consistency and accuracy of the ratings.


There are several ways to improve inter-rater reliability, including:

  1. Clear criteria and definitions: Ensure that the criteria and definitions used to evaluate the phenomenon are clear and unambiguous. This can be done through training, discussions, or reference materials.

  2. Standardised protocol: Provide a standardised protocol or form that guides the raters in their evaluations. This can include instructions, rating scales, and examples of what to look for.

  3. Rater training: Train the raters on how to use the protocol and how to apply the criteria consistently. This can include practice exercises for screening, feedback, and discussion.

  4. Rater monitoring: Monitor the raters during the evaluation process to ensure that they are applying the criteria consistently. This can include observing their evaluations, providing feedback, and resolving any disagreements.

  5. Blind ratings: Blind ratings can be used to improve inter-rater reliability by preventing raters from being influenced by the ratings of others. Covidence does this automatically.

  6. Pilot testing: Pilot testing can be used to identify any issues with the protocol or criteria before the actual evaluation process begins.

By using these methods, you can improve the consistency and accuracy of the ratings, which can lead to more reliable and valid research findings.