From "Diffusion of Laparoscopic Cholecystectomy in the Veterans Affairs Health Care System, 1991-1995" Effective Clinical Practice, March/April 1999. 2:49-55.

Figure 1. Rates of open and laparoscopic cholecystectomy by year in the Veterans Affairs system. The increase in the rate for all cholecystectomies is significant over time (P<0.001 by the chi-square test for linear trend)
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