Sequential monitoring of hospital adverse events when control charts fail : the example of fall injuries in hospitals

Barker, A., Morton, A., Gatton, M., Tong, E., & Clements, A. (2009) Sequential monitoring of hospital adverse events when control charts fail : the example of fall injuries in hospitals. Qual Saf Health Care, 18(6), pp. 473-477.

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To evaluate methods for monitoring monthly aggregated hospital adverse event data that display clustering, non-linear trends and possible autocorrelation.


Retrospective audit.


The Northern Hospital, Melbourne, Australia.


171,059 patients admitted between January 2001 and December 2006.


The analysis is illustrated with 72 months of patient fall injury data using a modified Shewhart U control chart, and charts derived from a quasi-Poisson generalised linear model (GLM) and a generalised additive mixed model (GAMM) that included an approximate upper control limit.


The data were overdispersed and displayed a downward trend and possible autocorrelation. The downward trend was followed by a predictable period after December 2003. The GLM-estimated incidence rate ratio was 0.98 (95% CI 0.98 to 0.99) per month. The GAMM-fitted count fell from 12.67 (95% CI 10.05 to 15.97) in January 2001 to 5.23 (95% CI 3.82 to 7.15) in December 2006 (p<0.001). The corresponding values for the GLM were 11.9 and 3.94. Residual plots suggested that the GLM underestimated the rate at the beginning and end of the series and overestimated it in the middle. The data suggested a more rapid rate fall before 2004 and a steady state thereafter, a pattern reflected in the GAMM chart. The approximate upper two-sigma equivalent control limit in the GLM and GAMM charts identified 2 months that showed possible special-cause variation.


Charts based on GAMM analysis are a suitable alternative to Shewhart U control charts with these data.

Impact and interest:

5 citations in Scopus
4 citations in Web of Science®
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ID Code: 75119
Item Type: Journal Article
Refereed: Yes
Additional Information: Barker, A
Morton, A
Gatton, M
Tong, E
Clements, A
Research Support, Non-U.S. Gov't
Quality & safety in health care
Qual Saf Health Care. 2009 Dec;18(6):473-7.
Additional URLs:
Keywords: hospital, adverse events, fall injuries, control chart, monitoring
DOI: 10.1136/qshc.2007.025601
ISSN: 1475-3901
Subjects: Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > PUBLIC HEALTH AND HEALTH SERVICES (111700) > Public Health and Health Services not elsewhere classified (111799)
Divisions: Current > QUT Faculties and Divisions > Faculty of Health
Current > Schools > School of Public Health & Social Work
Deposited On: 25 Aug 2014 00:59
Last Modified: 27 Aug 2014 00:51

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