Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
The correlation between the extraction time and the modified difficulty indices. A. The correlation between the extraction time and the half-up difficulty index. The correlation coefficient was 0.728, suggesting a strong positive correlation (P<0.001). B. The correlation between the extraction time and the half-up difficulty index. The correlation coefficient was 0.764, suggesting a strong positive correlation (P<0.001).
