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Research:
Boris Sobolev, Dale Mercer, Peter Brown, Mark FitzGerald, Diederick Jalink, and Ralph Shaw
Risk of emergency admission while awaiting elective cholecystectomy
CMAJ 2003; 169: 662-665 [Abstract] [Full text] [PDF]
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[Read eLetter] Drawing policy conclusions from uncontrolled studies
Alexander C. Tsai   (3 October 2003)

Drawing policy conclusions from uncontrolled studies 3 October 2003
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Alexander C. Tsai
Case Western Reserve University School of Medicine

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Re: Drawing policy conclusions from uncontrolled studies

act2{at}case.edu Alexander C. Tsai

Studying a population of adults being seen in clinic for biliary colic, Sobolev et al.(1) documented an association between waiting times and admissions for emergency cholecystectomy.

Because the patients were not randomized to the waiting list, however, readers should entertain the possibility that the observed association between waiting times and emergency admissions is driven by their association with a so-called "third variable." For example, the patients who end up on the waiting list may be sicker; if that is the case, then the observed association between waiting times and emergency admissions is actually driven by an unobserved association between health status and emergency admissions. Sobolev et al.(1) acknowledge in the discussion the possibility of confounding by patient morbidity, and they do attempt rudimentary adjustment for other potential confounding variables. However, even if they had access to better data on patient health status, the criticism of potential confouding would still plague their analysis.

Prior studies, none of which were cited by Sobolev et al.(1), have addressed this problem using econometric methodology(2-4). Hamilton, Hamilton, and Mayo(2) used an estimation strategy that accounted for unmeasured health differences and found no effect of waiting times on mortality for patients queuing for hip fracture surgery. Subsequent comparisons of hip fracture patients in the U.S. and Canada,(3,4) also accounting for the endogeneity of waiting time, arrived at a similar conclusion: lengthier waiting times did not affect mortality for patients queuing for hip fracture surgery.

Policymakers seeking to draw conclusions from the findings of Sobolev et al.(1) would be well advised to also consider these more sophisticated econometric analyses in their deliberations.

1. Sobolev B, Mercer D, Brown P, FitzGerald M, Jalink D, Shaw R. Risk of emergency admission while awaiting elective cholecystectomy. CMAJ. 2003 Sep 30;169(7):662-5.

2. Hamilton BH, Hamilton VH, Mayo NE. What are the costs of queuing for hip fracture surgery in Canada? J Health Econ. 1996 Apr;15(2):161-85.

3. Ho V, Hamilton BH, Roos LL. Multiple approaches to assessing the effects of delays for hip fracture patients in the United States and Canada. Health Serv Res. 2000 Mar;34(7):1499-518.

4. Hamilton BH, Ho V, Goldman DP. Queuing for surgery: is the U.S. or Canada worse off? Rev Econ Stat. 2000 May;82(2):297-308.

Conflict of Interest:

None declared