Reliability of league tables of in vitro fertilisation clinics: retrospective analysis of live birth ratesCommentary: How robust are rankings? The implications of confidence intervals
BMJ 1998; 316 doi: https://doi.org/10.1136/bmj.316.7146.1701 (Published 06 June 1998) Cite this as: BMJ 1998;316:1701
Abstract
Objective: To determine to what extent institutions carrying out in vitro fertilisation can reasonably be ranked according to their live birth rates.
Design: Retrospective analysis of prospectively collected data on live birth rate after in vitro fertilisation.
Setting: 52 clinics in the United Kingdom carrying out in vitro fertilisation over the period April 1994 to March 1995.
Main outcome measure: Estimated adjusted live birth rate for each clinic; their rank and its associated uncertainty.
Results: There were substantial and significant differences between the live birth rates of the clinics. There was great uncertainty, however, concerning the true ranks, particularly for the smaller clinics. Only one clinic could be confidently ranked in the bottom quarter according to this measure of performance. Many centres had substantial changes in rank between years, even though their live birth rate did not change significantly.
Conclusions: Even when there are substantial differences between institutions, ranks are extremely unreliable statistical summaries of performance and change in performance, particularly for smaller institutions. Any performance indicator should always be associated with a measure of sampling variability.
Key messages
Institutional ranks are extremely unreliable statistical summaries of performance
Institutions with smaller numbers of cases may be unjustifiably penalised or credited in comparison exercises
Additional statistical analysis may help to identify the few institutions worthy of review
Any performance indicator should always have an associated statistical sampling variability
Footnotes
- Accepted 17 December 1997
Reliability of league tables of in vitro fertilisation clinics: retrospective analysis of live birth rates
- E Clare Marshall, research student,
- David J Spiegelhalter, senior statistician (david.spiegelhalter{at}mrc-bsu.cam.ac.uk)
- MRC Biostatistics Unit, Institute of Public Health, Cambridge CB2 2SR
- Health Services Research Unit, Department of Public Health and Policy, London School of Hygiene and Tropical Medicine, London WC1E 7HT
- Correspondence to: Dr Spiegelhalter
- Accepted 17 December 1997
Abstract
Objective: To determine to what extent institutions carrying out in vitro fertilisation can reasonably be ranked according to their live birth rates.
Design: Retrospective analysis of prospectively collected data on live birth rate after in vitro fertilisation.
Setting: 52 clinics in the United Kingdom carrying out in vitro fertilisation over the period April 1994 to March 1995.
Main outcome measure: Estimated adjusted live birth rate for each clinic; their rank and its associated uncertainty.
Results: There were substantial and significant differences between the live birth rates of the clinics. There was great uncertainty, however, concerning the true ranks, particularly for the smaller clinics. Only one clinic could be confidently ranked in the bottom quarter according to this measure of performance. Many centres had substantial changes in rank between years, even though their live birth rate did not change significantly.
Conclusions: Even when there are substantial differences between institutions, ranks are extremely unreliable statistical summaries of performance and change in performance, particularly for smaller institutions. Any performance indicator should always be associated with a measure of sampling variability.
Key messages
Institutional ranks are extremely unreliable statistical summaries of performance
Institutions with smaller numbers of cases may be unjustifiably penalised or credited in comparison exercises
Additional statistical analysis may help to identify the few institutions worthy of review
Any performance indicator should always have an associated statistical sampling variability
Footnotes
- Accepted 17 December 1997
Commentary: How robust are rankings? The implications of confidence intervals
- Colin Sanderson, senior lecturer in health services research (c.sanderson{at}lshtim.ac.uk),
- Martin McKee, professor
- MRC Biostatistics Unit, Institute of Public Health, Cambridge CB2 2SR
- Health Services Research Unit, Department of Public Health and Policy, London School of Hygiene and Tropical Medicine, London WC1E 7HT
- Correspondence to: Dr Sanderson