Improving the quality of healthcare in Japan: a systematic review of procedural volume and outcome literature.

Though some policies have been implemented based on volume-outcome relationships in Japan, no studies systematically reviewed volume-outcome research conducted in Japan. Original data used in this study were obtained from MEDLINE searches using PubMed or from searches of the Ichushi database and complemented with manual searches. Two investigators reviewed and scored 13 articles, using a standard form to extract information regarding key study characteristics and results. Of the 13 studies we reviewed, 11 studies sought to detect the effects of hospital volume on outcomes while 2 examined the influence of individual physician volumes. Of the 13 studies, 9 studies (69.2%) indicated a statistically significant association between higher hospital volumes and better health outcomes. No study documented a statistically significant association between higher volumes and poorer outcomes. Higher review score is considered to be associated with significant association. The definition of low volume differed widely in each of the studies we reviewed. The 95%CI of healthcare outcomes is considerable even in studies that revealed a significant difference between volumes and outcomes. Higher hospital volumes are thought to be associated with better aggregate healthcare outcomes in Japan. For this reason, minimal-case-number standards might be effective to some extent. However, volume alone is not sufficient to predict the quality of healthcare. In addition, outcome-based evaluation might also be needed.