Het volume van chirurgische ingrepen en de impact ervan op ... - KCE

KCE Reports 113 Volume Outcome 33
However, it is not the volume of the restaurant that creates the higher quality, but the
higher quality that attracts higher volume of customers.
Figure 3.8: Two hypotheses of causality from Luft et al. 99
Luft et al. explored the plausibility of each hypothesis on a series of diagnoses and
procedures, and concluded that both explanations were valid, and that the relative
importance of the practice or referral explanation varies by diagnosis or procedure. 99
The policy implications of the two competing hypotheses are also very different. If the
observed pattern reflects only the « practice makes perfect » phenomenon,
concentrating patients in selected hospitals will improve outcomes. On the other hand,
if the observed pattern is entirely due to selective referral, the concentration of patients
is not necessary. As shown by Luft et al, the reality is often less black-and-white, with
hypotheses not being mutually exclusive. Given the substantial differences in policy
implications, it is important that the analyses try to distinguish both hypotheses.
Luft et al proposed two approaches to investigate which explanation of the two is the
more plausible. 99 The first approach is mainly descriptive, and the second uses
simultaneous equations modelling.
The first simple approach to explore the relation between volume and outcome is to
categorize hospitals by the number of patients in a particular diagnosis or procedure
category, and then to examine patterns of selected variables across volume and types of
patients. Luft et al proposed three indicators:
1. Transfer into the hospital. The proportion of patients transferred into one
hospital from another acute hospital is a direct measure of the selective
referral. Luft et al showed that for some procedures, there are marked
differences in transfer rates with respect to volume. The authors differentiate
the patterns as « strong increasing pattern », « weak increasing pattern », « U
shaped », « roughly flat » and « L-shaped ». The strong increasing trends are
consistent with the selective referral and inconsistent with the position that
practices makes perfect as the only explanation of the volume outcome
relation.
2. Transfer to another hospital: the proportion of patients discharged to
another hospital rather than to a convalescent facility or home is the flip side
of the in transfer rate. Luft shows that for most diagnoses and procedures
the transfer rate falls with volume.
3. The risk pattern of patients. This is the final piece of evidence with respect to
selective referral. An expected mortality rate based on patients’
characteristics can be computed for each hospital.