Complex interventions or complex systems? Implications for health economic evaluation
BMJ 2008; 336 doi: https://doi.org/10.1136/bmj.39569.510521.AD (Published 05 June 2008) Cite this as: BMJ 2008;336:1281
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New methods of measuring and reporting the outcome of change in health and social care systems are needed, because the average stay of discharged patients masks the process of care. Not simply because the distribution of length of stay is skewed, but also because internal and external factors influence the outcome of inpatient care.
Seeking to explain the outcome of change in a New Zealand acute medical service we mapped the pattern of daily bed occupancy and used this to show the changing pattern of bed closure and bed borrowing. We also used the percentile distribution of length of stay and destination discharge to explain and explore the outcome of fast-tracking the process of care.
The data analysed included all admissions between 1992 and 2003. During these years there have been a series of bed crises with different explanations as to cause. Now, in 2008, there is a prevailing bed crisis which still needs to be resolved
The first bed crisis followed bed closure. In 1996 fast-tracking acute medical care resolved that crisis. Percentile analysis showed that comprehensive change in medical staff behaviour established a new stable state in the process of care,in which geriatric medicine also played a part, as a secondary recovery and rehabilitation service.
Whether this new style of behaviour service would have been sustainable is unknown as further bed closures and relocation of geriatric medical services to the teaching hospital site led to an ongoing bed crisis that still needs to be resolved. Also length of stay is increasing as the problem faced now concerns availability of services in the community. This is out with the control of the hospital staff.
Full details of the study and methods are in the Australian Health Review 1.
1. Rae B, Busby W, Millard PH. Fast-tracking acute hospital care — from bed crisis to bed crisis. Australian Health Review 2007;31(1):50-62.
Competing interests: None declared
Competing interests: No competing interests
Dynamic vs static aspects of nonlinearities
In physiology, to cite but one example, the pupillary reflex to light is inverted in the eye's paradoxically constrictive response to a darkness 'flash', i.e.,a brief reduction then return of light intensity to its previous level. In the physical world, the phenomenon called 'stall' nullifies an airplane wing's aerodynamic lift when the angle of climb exceeds a theshold value. These and other dynamic non-linearities tend to lurk unrecognised within certain complex systems, to appear only during or shortly after their encounter with specific temporal patterns of input. Dynamic non-linearities change familiar rules of operation into a different set of rules of operation that can be confusingly unfamiliar and sometimes hazardous.
References and a more full discussion of these matters can be found in: Chapter 13 of "Simulation for designing clinical trials". Eds: Ko HC, Duffull S. New York: Marcel Dekker, 2002, pp 245-69. ISBN 0-8247-0862-8
Competing interests: shareholder of AARDEX Ltd, which makes & sells electronic medication event monitors to compile drug dosing histories in ambulatory patients.
Competing interests: No competing interests