The I’-chart: a preliminary investigation of an improved individuals chart for quality improvement and control

Clicks: 22
ID: 330032
2026
Free PDF
Article Quality & Performance Metrics
Overall Quality
Not rated
Combines reader engagement with the AI quality analysis. This article has not been analysed, so there is no overall score — reader engagement is measured and shown alongside.
AI Quality Assessment
Not analyzed
Readership in this journal
Emerging

Ranked #78 of 154 articles by views in International journal for quality in health care : journal of the International Society for Quality in Health Care

Most read Least read

Bar heights use a square-root scale. Only the 120 most-read articles are drawn; the journal has 154 in total.

Mint this article as an NFT
Not yet minted

Create a permanent, verifiable on-chain record of this article on the Scimatic Network. The NFT is held in your Journament account, and you can withdraw it to your own wallet at any time.

5 SUSD one-off · no wallet required
Sign in to mint
Abstract
BACKGROUND: Statistical Process Control (SPC) charts are widely used in healthcare to monitor and improve quality. Selecting the appropriate chart can be challenging because healthcare data often comprise subgroup summary measures derived from varying numbers of observations. The traditional Individuals (I-) chart is popular because of its simplicity but assumes constant subgroup sizes, an assumption frequently violated in practice. This can lead to inappropriate control limits and misleading interpretation. We describe the I'-chart, an extension of the traditional I-chart that accommodates varying subgroup sizes while remaining applicable to both measurement and attribute data and present a preliminary evaluation of its performance. METHODS: The I'-chart was evaluated using a range of simulated and real-world healthcare datasets to address three practical questions: (a) How does the I'-chart compare with the traditional I-chart when subgroup sizes are constant? (b) How does the I'-chart accommodate varying subgroup sizes? (c) How does the I'-chart compare with other established SPC charts? RESULTS: (a) The I'-chart produced identical results to the traditional I-chart when subgroup sizes were constant, confirming that it generalises the conventional I-chart. (b) When subgroup sizes varied, the I'-chart adjusted the control limits according to subgroup size, making differences in data precision explicit and, in a healthcare example, changing an apparent special-cause signal into expected common-cause variation. (c) The control limits produced by the I'-chart using simulated data were broadly comparable with those from established SPC charts, including the Xbar-chart for measurement data and Laney's P'- and U'-charts for attribute data. CONCLUSION: The I'-chart has superior design properties to the traditional I-chart while retaining its simplicity and ease of interpretation. By explicitly accounting for varying subgroup sizes, it addresses an important limitation of the traditional I-chart. Our findings support replacing the traditional I-chart whenever subgroup summary data with varying subgroup sizes are analysed. Although further methodological and empirical evaluation is required to establish its operating characteristics and define its role alongside other SPC charts, the examples presented suggest that the I'-chart produces results comparable with established SPC methods while providing a single, generalisable framework for analysing subgroup summary data.
Reference Key
openalex_W7214581468 Use this key to autocite in the manuscript while using SciMatic Manuscript Manager or Thesis Manager
Authors Jacob Anhøj, Wayne A. Taylor, Mohammed Amin Mohammed
Journal International journal for quality in health care : journal of the International Society for Quality in Health Care
Year 2026
DOI
10.1093/intqhc/mzag159
URL
https://doi.org/10.1093/intqhc/mzag159
Keywords Keywords not found

Citations

No citations found. To add a citation, contact the admin at info@scimatic.org

Comments

No comments yet. Be the first to comment on this article.