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The Lancet. A new direction for hepatitis C. Lancet 2014; 383: 1270. Gluud C, Brok J, Gong Y, Koretz RL. Hepatology may have problems with putative surrogate outcome measures. J Hepatol 2007; 46: 734–42. Brok J, Gluud LL, Gluud C. Ribavirin plus interferon versus interferon for chronic hepatitis C. Cochrane Database Syst Rev 2010; 1: CD005445. Hauser G, Awad T, Brok J, et al. Peginterferon plus ribavirin versus interferon plus ribavirin for chronic hepatitis C. Cochrane Database Syst Rev 2014; 2: CD005441. Koretz RL, Pleguezuelo M, Arvaniti V, et al. Interferon for interferon nonresponding and relapsing patients with chronic hepatitis C. Cochrane Database Syst Rev 2013; 1: CD003617. Gurusamy KS, Wilson E, Koretz RL, et al. Is sustained virological response a marker of treatment efficacy in patients with chronic hepatitis C viral infection with no response or relapse to previous antiviral intervention? PLoS One 2013; 8: e83313.
Mortality from ruptured abdominal aortic aneurysms We have several questions regarding the comparison of ruptured abdominal aortic aneurysm mortality rates in the USA and England (March 15, p 963).1 Having identified independent predictors of mortality in both countries such as hospital volume and teaching hospital status, why were these con founders not included in the age and sex-stratified model comparing the odds of mortality between countries? Furthermore, with the significant difference in the rates of intervention, why was intervention not added to this model to evaluate its contribution to the differences observed between countries? This addition would give more confidence in the conclusion that the difference in mortality is due to the difference in intervention rates, and not other confounders. In view of the discordant rate of discharge to another health-care facility, an analysis that takes into account a shorter observation time of 7–10 days, or one that censors observations at discharge might be more appropriate, because the outcomes of patients www.thelancet.com Vol 383 June 21, 2014
following transfer to another facility are unknown. The Nationwide Inpatient Sample is not a longitudinally linked dataset, and does not allow patients to be tracked in time. This risks multiple observations of a single ruptured abdominal aortic aneurysm episode in the sample. Would the authors please comment on how patients who were transferred between institutions either preoperatively or postoperatively were excluded or accounted for? Finally, because the Nationwide Inpatient Sample is a 20% sample, would an unweighted sample have been more accurate for the purposes of statistical comparison with Hospital Episodes Statistics, which is an unweighted, near 100% sample? We declare no competing interests.
*Aruna Munasinghe, Mantaj Brar, Omar Faiz [email protected] Imperial College London, St Mary’s Hospital, London W21NY, UK (AM); London School of Hygiene & Tropical Medicine, London , UK (MB); and St Mark’s Academic Institute, London, UK (OF) 1
Karthikesalingam A, Holt PJ, Vidal-Diez A, et al. Mortality from ruptured abdominal aortic aneurysms: clinical lessons from a comparison of outcomes in England and the USA. Lancet 2014; 383: 963–69.
Authors’ reply We thank Aruna Munasinghe and colleagues for their interest in our work comparing ruptured abdominal aortic aneurysm mortality rates in the USA and England.1 We exercised caution when constructing statistical models that combined data from the USA and UK to mitigate concerns that differences between health-care systems might lead to inaccurate assumptions in a single model. Although age and sex are consistently defined, other patient-level characteristics might be subject to systematic differences in coding between countries. Similarly, although Munasinghe and colleagues suggested the inclusion of hospital-level factors to improve an international model, we were
concerned that teaching hospital status or procedural volume might be variably defined in each healthcare system. These factors describe different effects in the USA and England, and would therefore risk confounding and inaccuracy if included in international riskadjustment. We agree that it is important to acknowledge the potential effect of the international differences in discharge policies, and have already stressed this as a limitation of our work. However, we feel that an analysis restricted to 7-day mortality might be misleading and would not adequately address this limitation. For patients with ruptured abdominal aortic aneurysm there is an increasing body of evidence that critical care provision plays an important part in survival, and 90day mortality would therefore be a more informative measure. 2 We are engaged in active collaborative projects to identify international discrepancies in this outcome between the UK and other healthcare systems where mortality data are available beyond hospital discharge. We also aim to do further studies with international 100% samples. A l th o u gh th e N ationw id e Inpatient Sample does not allow longitudinal linkage, each case in the sample includes a description of the admission source and discharge destination. We did a sensitivity analysis by matching patients that were transferred to or from another US hospital by age, income quartile, same or previous month of admission, year of admission, and hospital region. 20 of 20 838 (0·09%) US patients met the matching criteria and could potentially have been double-counted; exclusion of these patients did not alter our findings. Even if there was any further unmeasurable bias in favour of double-counting US patients in our study, this would only lower the
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The Lancet. A new direction for hepatitis C. Lancet 2014; 383: 1270. Gluud C, Brok J, Gong Y, Koretz RL. Hepatology may have problems with putative surrogate outcome measures. J Hepatol 2007; 46: 734–42. Brok J, Gluud LL, Gluud C. Ribavirin plus interferon versus interferon for chronic hepatitis C. Cochrane Database Syst Rev 2010; 1: CD005445. Hauser G, Awad T, Brok J, et al. Peginterferon plus ribavirin versus interferon plus ribavirin for chronic hepatitis C. Cochrane Database Syst Rev 2014; 2: CD005441. Koretz RL, Pleguezuelo M, Arvaniti V, et al. Interferon for interferon nonresponding and relapsing patients with chronic hepatitis C. Cochrane Database Syst Rev 2013; 1: CD003617. Gurusamy KS, Wilson E, Koretz RL, et al. Is sustained virological response a marker of treatment efficacy in patients with chronic hepatitis C viral infection with no response or relapse to previous antiviral intervention? PLoS One 2013; 8: e83313.
Mortality from ruptured abdominal aortic aneurysms We have several questions regarding the comparison of ruptured abdominal aortic aneurysm mortality rates in the USA and England (March 15, p 963).1 Having identified independent predictors of mortality in both countries such as hospital volume and teaching hospital status, why were these con founders not included in the age and sex-stratified model comparing the odds of mortality between countries? Furthermore, with the significant difference in the rates of intervention, why was intervention not added to this model to evaluate its contribution to the differences observed between countries? This addition would give more confidence in the conclusion that the difference in mortality is due to the difference in intervention rates, and not other confounders. In view of the discordant rate of discharge to another health-care facility, an analysis that takes into account a shorter observation time of 7–10 days, or one that censors observations at discharge might be more appropriate, because the outcomes of patients www.thelancet.com Vol 383 June 21, 2014
following transfer to another facility are unknown. The Nationwide Inpatient Sample is not a longitudinally linked dataset, and does not allow patients to be tracked in time. This risks multiple observations of a single ruptured abdominal aortic aneurysm episode in the sample. Would the authors please comment on how patients who were transferred between institutions either preoperatively or postoperatively were excluded or accounted for? Finally, because the Nationwide Inpatient Sample is a 20% sample, would an unweighted sample have been more accurate for the purposes of statistical comparison with Hospital Episodes Statistics, which is an unweighted, near 100% sample? We declare no competing interests.
*Aruna Munasinghe, Mantaj Brar, Omar Faiz [email protected] Imperial College London, St Mary’s Hospital, London W21NY, UK (AM); London School of Hygiene & Tropical Medicine, London , UK (MB); and St Mark’s Academic Institute, London, UK (OF) 1
Karthikesalingam A, Holt PJ, Vidal-Diez A, et al. Mortality from ruptured abdominal aortic aneurysms: clinical lessons from a comparison of outcomes in England and the USA. Lancet 2014; 383: 963–69.
Authors’ reply We thank Aruna Munasinghe and colleagues for their interest in our work comparing ruptured abdominal aortic aneurysm mortality rates in the USA and England.1 We exercised caution when constructing statistical models that combined data from the USA and UK to mitigate concerns that differences between health-care systems might lead to inaccurate assumptions in a single model. Although age and sex are consistently defined, other patient-level characteristics might be subject to systematic differences in coding between countries. Similarly, although Munasinghe and colleagues suggested the inclusion of hospital-level factors to improve an international model, we were
concerned that teaching hospital status or procedural volume might be variably defined in each healthcare system. These factors describe different effects in the USA and England, and would therefore risk confounding and inaccuracy if included in international riskadjustment. We agree that it is important to acknowledge the potential effect of the international differences in discharge policies, and have already stressed this as a limitation of our work. However, we feel that an analysis restricted to 7-day mortality might be misleading and would not adequately address this limitation. For patients with ruptured abdominal aortic aneurysm there is an increasing body of evidence that critical care provision plays an important part in survival, and 90day mortality would therefore be a more informative measure. 2 We are engaged in active collaborative projects to identify international discrepancies in this outcome between the UK and other healthcare systems where mortality data are available beyond hospital discharge. We also aim to do further studies with international 100% samples. A l th o u gh th e N ationw id e Inpatient Sample does not allow longitudinal linkage, each case in the sample includes a description of the admission source and discharge destination. We did a sensitivity analysis by matching patients that were transferred to or from another US hospital by age, income quartile, same or previous month of admission, year of admission, and hospital region. 20 of 20 838 (0·09%) US patients met the matching criteria and could potentially have been double-counted; exclusion of these patients did not alter our findings. Even if there was any further unmeasurable bias in favour of double-counting US patients in our study, this would only lower the
Simon Fraser/Freeman Hospital, Newcastle/ Science Photo Library
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