Papers

Effect of correcting outcome data for case mix: an example from stroke medicine

^a University of Edinburgh, Department of Clinical Neurosciences, Western General Hospital, Edinburgh EH4 2XU

Correspondence to: Dr Davenport.

Abstract

Objective: To show the influence of variations in case mix on clinical outcome indicators for patients admitted to hospital with acute stroke.
Design: "Before and after" cohort study, with prospective, consecutive identification of patients and prospective follow up; multiple logistic regression analyses to correct for case mix variations.
Setting: University teaching hospital.
Subjects: 216 patients with stroke identified before the introduction of an organised stroke service, and 252 patients with stroke identified after its introduction.
Main outcome measures: Case fatality at 30 days and 12 months; for survivors at 12 months, proportions of patients who were independent (according to the Oxford handicap scale) and of those living at home.
Results: Crude outcome data suggested that patients in the cohort identified after the introduction of the stroke service were significantly more likely to be alive, independent, and living at home than patients managed before the stroke service. After adjustment for age and sex these "improvements" were less impressive but still significant. After adjustment for many other possible prognostic indicators, however, the differences between the two groups for all four outcomes were non-significant, suggesting that the "improvements" may have been entirely due to differences in case mix between the two cohorts, rather than the new stroke service.
Conclusions: Variations in case mix have a crucial influence on the interpretation of outcome data, and this is particularly important in non-randomised comparative studies. Such studies, comparing performance within and between different provider units, are likely to become increasingly common in the new reformed NHS. To allow meaningful interpretation, these studies must try to correct for case mix.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    StumbleUpon    Technorati    What's this?

This article has been cited by other articles:

• Zhu, H. F., Newcommon, N. N., Cooper, M. E., Green, T. L., Seal, B., Klein, G., Weir, N. U., Coutts, S. B., Watson, T., Barber, P. A., Demchuk, A. M., Hill, M. D., for the Calgary Stroke Program, (2009). Impact of a Stroke Unit on Length of Hospital Stay and In-Hospital Case Fatality. Stroke 40: 18-23 [Abstract] [Full text]  
• De Wit, L., Putman, K., Schuback, B., Komarek, A., Angst, F., Baert, I., Berman, P., Bogaerts, K., Brinkmann, N., Connell, L., Dejaeger, E., Feys, H., Jenni, W., Kaske, C., Lesaffre, E., Leys, M., Lincoln, N., Louckx, F., Schupp, W., Smith, B., De Weerdt, W. (2007). Motor and Functional Recovery After Stroke: A Comparison of 4 European Rehabilitation Centers. Stroke 38: 2101-2107 [Abstract] [Full text]  
• Seenan, P., Long, M., Langhorne, P. (2007). Stroke Units in Their Natural Habitat: Systematic Review of Observational Studies. Stroke 38: 1886-1892 [Abstract] [Full text]  
• Gray, L J, Sprigg, N, Bath, P M W, Sorensen, P, Lindenstrom, E, Boysen, G, De Deyn, P P, Friis, P, Leys, D, Marttila, R, Olsson, J-E, O'Neill, D, Ringelstein, B, van der Sande, J-J, Turpie, A G G, for the TAIST Investigators, (2006). Significant variation in mortality and functional outcome after acute ischaemic stroke between western countries: data from the tinzaparin in acute ischaemic stroke trial (TAIST). J. Neurol. Neurosurg. Psychiatry 77: 327-333 [Abstract] [Full text]  
• van Exel, N.J.A., Koopmanschap, M.A., Scholte op Reimer, W., Niessen, L.W., Huijsman, R. (2005). Cost-effectiveness of integrated stroke services. QJM 98: 415-425 [Abstract] [Full text]  
• Walsh, K, Gompertz, P H, Rudd, A G (2002). Stroke care: how do we measure quality?. Postgrad. Med. J. 78: 322-326 [Abstract] [Full text]  
• Wolfe, C., Rudd, A., Dennis, M., Warlow, C., Langhorne, P. (2001). Taking acute stroke care seriously. BMJ 323: 5-6 [Full text]  
• Grieve, R., Hutton, J., Bhalla, A., Rastenyte, D., Ryglewicz, D., Sarti, C., Lamassa, M., Giroud, M., Dundas, R., Wolfe, C.D.A. (2001). A Comparison of the Costs and Survival of Hospital-Admitted Stroke Patients Across Europe. Stroke 32: 1684-1691 [Abstract] [Full text]  
• Weir, N., Dennis, M. S. (2001). Towards a National System for Monitoring the Quality of Hospital-Based Stroke Services. Stroke 32: 1415-1421 [Abstract] [Full text]  
• McKevitt, C., Dundas, R., Wolfe, C. (2001). Two Simple Questions to Assess Outcome After Stroke : A European Study. Stroke 32: 681-686 [Abstract] [Full text]  
• Man-Son-Hing, M., Laupacis, A., O'Connor, A. M., Coyle, D., Berquist, R., McAlister, F. (2000). Patient Preference-based Treatment Thresholds and Recommendations: A Comparison of Decision-analytic Modeling with the Probability-tradeoff Technique. Med Decis Making 20: 394-402 [Abstract]  
• Williams, L. S., Yilmaz, E. Y., Lopez-Yunez, A. M. (2000). Retrospective Assessment of Initial Stroke Severity With the NIH Stroke Scale. Stroke 31: 858-862 [Abstract] [Full text]  
• Freburger, J. K (1999). An Analysis of the Relationship Between the Utilization of Physical Therapy Services and Outcomes for Patients With Acute Stroke. ptjournal 79: 906-918 [Abstract] [Full text]  
• Wolfe, C. D. A., Tilling, K., Beech, R., Rudd, A. G. (1999). Variations in Case Fatality and Dependency From Stroke in Western and Central Europe. Stroke 30: 350-356 [Abstract] [Full text]  
• Lane, R., Burrell, K., Dennis, C. (1997). Study confirms results of systematic review of care in stroke unit. BMJ 315: 881-881 [Full text]  
• Kendrick, S., Bain, M. (1996). Further studies are needed to assess current outcome indicators. BMJ 313: 1006-1006 [Full text]  
• Barer, D., Ellul, J., Watkins, C. (1996). Correcting outcome data for case mix in stroke medicine. BMJ 313: 1005c-1006 [Full text]  
• Mant, J., Hicks, N. R, Fletcher, J. (1996). Study should have had more patients or longer time scale. BMJ 313: 1006a-1006 [Full text]  
• Evans, R. (1996). American guidelines on managed care are not the answer. BMJ 313: 946b-946 [Full text]