RESEARCH
Including post-discharge mortality in calculation of hospital standardised mortality ratios: retrospective analysis of hospital episode statistics Maurice E Pouw,1 L M Peelen,2 K G M Moons,2 C J Kalkman,1 H F Lingsma3
Cite this as: BMJ 2013;347:f5913 doi: 10.1136/bmj.f5913
This is a summary of a paper that was published on bmj.com as BMJ 2013;347:f5913
bmj.com/multimedia ̻̻Watch a video abstract on this paper at bmj.com/ multimedia/video
SUMMARY ANSWER Selecting mortality timeframes that include the postdischarge period changes the standardised mortality ratios of individual hospitals and affects judgments about performance. WHAT IS KNOWN AND WHAT THIS PAPER ADDS Hospitals with a low in-hospital standardised mortality ratio are regarded as having a high degree of quality of care. In-hospital standardised mortality ratio and early postdischarge mortality were inversely associated, suggesting that low in-hospital mortality may reflect high postdischarge mortality instead of the assumed high quality of care.
Participants and setting We examined 1 228 815 patient discharges from 60 hospitals in the Netherlands in the period 2008-10. Design We did a retrospective analysis of routinely collected hospital data. We calculated standardised mortality ratios by comparing observed deaths with deaths predicted by a case mix adjustment method. These data were linked to the Dutch population register by Statistics Netherlands to allow inclusion of deaths after discharge. Primary outcome(s) The standardised mortality ratios were calculated using three different timeframes for observed mortality: from admission to discharge (in-hospital ratio), from admission to 30 days after admission (30 days post-admission ratio), and from admission to 30 days after discharge (30 days post-discharge ratio). Main results and the role of chance We classified hospitals into “worse than expected,” “conforms to expected,” and “better than expected” on the basis of the three standardised mortality ratios. Compared with in-hospital standardised mortality ratio, 20 (33%) hospitals were categorised differently with the 30 days post-admission ratio and 13 (22%) with the 30 days postdischarge ratio. The overall variation in standardised mortality ratios was smaller with the 30 days post-admission or 30 days post-discharge ratios than with the in-hospital
BMJ | 2 NOVEMBER 2013 | VOLUME 347
Number of hospitals
Department of Anesthesiology, University Medical Center Utrecht, Heidelberglaan 100, P O Box 85500, 3508 GA Utrecht, Netherlands 2 Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht, Netherlands 3 Department of Public Health, Erasmus MC, P O Box 2040, 3000 CA Rotterdam, Netherlands Correspondence to: M E Pouw [email protected]
Distributions of hospitals according to in-hospital standardised mortality ratio (SMR), 30 days post-admission SMR, and 30 days post-discharge SMR 25
In-hospital SMR
20 15 10 5 0
Number of hospitals
1
STUDY QUESTION To assess whether including mortality (shortly) after discharge affects the standardised mortality ratios of individual hospitals and the overall variation between hospitals in such ratios.
25
30 days post-admission SMR
20 15 10 5 0
Number of hospitals
ЖЖEDITORIAL by Nicoll and colleagues
25
30 days post-discharge SMR
20 15 10 5 0 55
65
75
85
95
105
115
125
SMR
ratio. Furthermore, in-hospital standardised mortality ratio and mortality shortly after discharge were inversely associated (Pearson correlation coefficient −0.37; P=0.004), suggesting discharge bias. Low in-hospital mortality at least partly reflects a high post-discharge mortality and not only a high degree of quality of care.
Bias, confounding, and other reasons for caution Because the administrative data used for this study were pseudonymised, approximately 10% of the discharges could not be linked. Generalisability to other populations If hospital mortality is used as a performance measure, guarding against bias and reducing the potential for “gaming” is essential. Our study suggests that standardised mortality ratios including post-discharge mortality are less vulnerable to discharge bias than are in-hospital standardised mortality ratios and are therefore preferable. Study funding/potential competing interests The study was commissioned by the Dutch Ministry of Health, Welfare and Sport.
13
Copyright of BMJ: British Medical Journal is the property of BMJ Publishing Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
Including post-discharge mortality in calculation of hospital standardised mortality ratios: retrospective analysis of hospital episode statistics Maurice E Pouw,1 L M Peelen,2 K G M Moons,2 C J Kalkman,1 H F Lingsma3
Cite this as: BMJ 2013;347:f5913 doi: 10.1136/bmj.f5913
This is a summary of a paper that was published on bmj.com as BMJ 2013;347:f5913
bmj.com/multimedia ̻̻Watch a video abstract on this paper at bmj.com/ multimedia/video
SUMMARY ANSWER Selecting mortality timeframes that include the postdischarge period changes the standardised mortality ratios of individual hospitals and affects judgments about performance. WHAT IS KNOWN AND WHAT THIS PAPER ADDS Hospitals with a low in-hospital standardised mortality ratio are regarded as having a high degree of quality of care. In-hospital standardised mortality ratio and early postdischarge mortality were inversely associated, suggesting that low in-hospital mortality may reflect high postdischarge mortality instead of the assumed high quality of care.
Participants and setting We examined 1 228 815 patient discharges from 60 hospitals in the Netherlands in the period 2008-10. Design We did a retrospective analysis of routinely collected hospital data. We calculated standardised mortality ratios by comparing observed deaths with deaths predicted by a case mix adjustment method. These data were linked to the Dutch population register by Statistics Netherlands to allow inclusion of deaths after discharge. Primary outcome(s) The standardised mortality ratios were calculated using three different timeframes for observed mortality: from admission to discharge (in-hospital ratio), from admission to 30 days after admission (30 days post-admission ratio), and from admission to 30 days after discharge (30 days post-discharge ratio). Main results and the role of chance We classified hospitals into “worse than expected,” “conforms to expected,” and “better than expected” on the basis of the three standardised mortality ratios. Compared with in-hospital standardised mortality ratio, 20 (33%) hospitals were categorised differently with the 30 days post-admission ratio and 13 (22%) with the 30 days postdischarge ratio. The overall variation in standardised mortality ratios was smaller with the 30 days post-admission or 30 days post-discharge ratios than with the in-hospital
BMJ | 2 NOVEMBER 2013 | VOLUME 347
Number of hospitals
Department of Anesthesiology, University Medical Center Utrecht, Heidelberglaan 100, P O Box 85500, 3508 GA Utrecht, Netherlands 2 Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht, Netherlands 3 Department of Public Health, Erasmus MC, P O Box 2040, 3000 CA Rotterdam, Netherlands Correspondence to: M E Pouw [email protected]
Distributions of hospitals according to in-hospital standardised mortality ratio (SMR), 30 days post-admission SMR, and 30 days post-discharge SMR 25
In-hospital SMR
20 15 10 5 0
Number of hospitals
1
STUDY QUESTION To assess whether including mortality (shortly) after discharge affects the standardised mortality ratios of individual hospitals and the overall variation between hospitals in such ratios.
25
30 days post-admission SMR
20 15 10 5 0
Number of hospitals
ЖЖEDITORIAL by Nicoll and colleagues
25
30 days post-discharge SMR
20 15 10 5 0 55
65
75
85
95
105
115
125
SMR
ratio. Furthermore, in-hospital standardised mortality ratio and mortality shortly after discharge were inversely associated (Pearson correlation coefficient −0.37; P=0.004), suggesting discharge bias. Low in-hospital mortality at least partly reflects a high post-discharge mortality and not only a high degree of quality of care.
Bias, confounding, and other reasons for caution Because the administrative data used for this study were pseudonymised, approximately 10% of the discharges could not be linked. Generalisability to other populations If hospital mortality is used as a performance measure, guarding against bias and reducing the potential for “gaming” is essential. Our study suggests that standardised mortality ratios including post-discharge mortality are less vulnerable to discharge bias than are in-hospital standardised mortality ratios and are therefore preferable. Study funding/potential competing interests The study was commissioned by the Dutch Ministry of Health, Welfare and Sport.
13
Copyright of BMJ: British Medical Journal is the property of BMJ Publishing Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
