Crude versus case-mix-adjusted control charts for safety monitoring in thyroid surgery.
BACKGROUND
Patient-safety monitoring based on health-outcome indicators can lead to misinterpretation of changes in case mix. This study aimed to compare the detection of indicator variations between crude and case-mix-adjusted control charts using data from thyroid surgeries.


METHODS
The study population included each patient who underwent thyroid surgery in a teaching hospital from January 2006 to May 2008. Patient safety was monitored according to two indicators, which are immediately recognisable postoperative complications: recurrent laryngeal nerve palsy and hypocalcaemia. Each indicator was plotted monthly on a p-control chart using exact limits. The weighted κ statistic was calculated to measure the agreement between crude and case-mix-adjusted control charts.


RESULTS
We evaluated the outcomes of 1405 thyroidectomies. The overall proportions of immediate recurrent laryngeal nerve palsy and hypocalcaemia were 7.4% and 20.5%, respectively. The proportion of agreement in the detection of indicator variations between the crude and case-mix-adjusted p-charts was 95% (95% CI 85% to 99%). The strength of the agreement was κ = 0.76 (95% CI 0.54 to 0.98). The single special cause of variation that occurred was only detected by the case-mix-adjusted p-chart.


CONCLUSIONS
There was good agreement in the detection of indicator variations between crude and case-mix-adjusted p-charts. The joint use of crude and adjusted charts seems to be a reasonable approach to increase the accuracy of interpretation of variations in outcome indicators.
Duclos
Antoine
A
Unité d'Étude des Pratiques Professionnelles, Hospices Civils de Lyon, Pôle d'Information Médicale Évaluation Recherche, 162 avenue Lacassagne, F-69424 Lyon Cedex 03, France. antoineduclos@yahoo.fr
Voirin
Nicolas
N
Touzet
Sandrine
S
Soardo
Pietro
P
Schott
Anne-Marie
AM
Colin
Cyrille
C
Peix
Jean-Louis
JL
Lifante
Jean-Christophe
JC
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D003953:Diagnosis-Related Groups; D005260:Female; D019538:Health Care Surveys; D006784:Hospitals, Teaching; D006801:Humans; D008297:Male; D008499:Medical Records; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D011446:Prospective Studies; D020379:Risk Adjustment; D017751:Safety Management; D013961:Thyroid Gland / Q000601:surgery*; D055815:Young Adult