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

KCE Reports 113 Volume Outcome 21
3 CRITICAL REVIEW OF METHODS TO
ASSESS THE VOLUME OUTCOME
RELATIONSHIP
3.1 INTRODUCTION
After considering the available evidence on the volume-outcome relationship, it is
important to address a series of more methodological questions. These questions
include: the completeness and reliability of administrative data, the determination of the
volume (surgeon or centre), the statistical methods used, the need for adjustment for
case-mix and the causal linkage. This will help not only to place individual studies in
perspective, but also to understand why findings may vary across studies. 82
3.2 RESEARCH QUESTION
The second research question of this project is the following:
What are the different statistical methods used in the literature to assess the volume-outcome
relationship in the health care context, and which of these methods specifically assess the
question of the causality?
The aim of this chapter is to guide the reader through the different statistical
methodologies that have been used so far in that area, to critically assess these methods
(pros and cons), and to provide a list of useful methodological references.
3.3 METHODS
3.3.1 Search strategy to select articles
The purpose of this review was to identify methods used to analyze the volumeoutcome
relationship in the health care context. The limitations of such review need to
be acknowledged. While a systematic search of the literature is fully appropriate when
answering questions about clinical effects (as in the first question), such search becomes
quickly tricky when the aim is to review methods. First because systematic search
always rely to some extend to the quality and consistency of the coding of the
keywords, and the usual clinical databases (Medline and Embase) are meant for that
purpose (keywords not specific enough). Second because good methodological
references are often books, not articles, discussing methods that are not specific to the
volume outcome relationship but can be used to address it. Therefore, the search was
less systematic than in the first chapter, and served mainly to identify and describe the
methods used in the volume outcome literature.
Our first step was thus to identify important key words used in analysis of volumeoutcome
studies. To that end, eight journals with strong methodological emphasis
were searched (Statistics in Medicine, Statistical Methods in Medical Research,
Biometrics, Journal of Clinical Epidemiology, Journal of Epidemiology and Community
Health, Controlled Clinical Trials, Clinical Trials, Journal of biopharmaceutical statistics),
with “volume OR outcome” as text in the title, abstract, keywords and text. Based on
the articles selected, a list of keywords was identified, and the MESH equivalent of these
keywords was searched.
The results are:
• ("Diagnosis-Related Groups"[Mesh] OR "Risk Adjustment"[Mesh])
• "Cluster Analysis"[Mesh]
• "Causality"[Mesh]
• "Longitudinal Studies"[Mesh]
Because not all keywords had a MESH-equivalent, some searches were also based on
text only:
• instrumental
• threshold