Hospital volume stratification using stratum-specific likelihood ratios for pancreatectomy

Recent literature suggests that volume-outcome associations for pancreatectomy have attenuated over time, leading some researchers to question the continued relevance of volume thresholds. However, this perceived attenuation may reflect the methodological limitations of single, binary cutoffs rather than a true weakening of the underlying relationship. Stratum-specific likelihood ratios (SSLRs) generate multiple empirically derived volume strata that may detect persistent gradients that are obscured by binary stratification. The objectives of this study were to (i) define volume strata for pancreatectomy using SSLR, (ii) assess the robustness of these strata across multiple outcomes, and (iii) examine whether the association persists in modern cohorts.

Patients who underwent pancreatectomy between 2004 and 2021 were identified using the National Cancer Database. The volume strata were defined by SSLR based on the 90-day postoperative mortality. The temporal threshold stability was assessed by stratified outcome analysis (chi-squared test).

Overall, 61,920 patients underwent pancreatectomy at 982 facilities with a 90-day mortality rate of 5.4%. SSLR analysis yielded 6 volume strata: ≤3, 4 to 9, 10 to 20, 21 to 47, 48 to 120, and ≥121 procedures/year with decreasing 90-day mortality (≤3: 11%; 4-9: 7.3%; 10-20: 6.1%; 21-47: 4.2%; 48-120: 3.3%; ≥121: 2.3%; P <.001). The optimized threshold of 21 procedures/year was identified based on SSLR. Temporal stratification into 5-year periods (2006-2010, 2011-2015, and 2016-2020) demonstrated persistent volume-outcome associations across volume strata (P <.001).

SSLR reveals persistent volume-outcome associations for pancreatectomy across multiple empirically derived strata, even in contemporary data. These findings suggest that reports of an attenuated volume-outcome relationship may reflect limitations of single, static cutoffs rather than true weakening of this association.