https://cis.temple.edu/~latecki/Courses/CIS2166-Fall16/Lectures/MatrixAlg1.pdf
A matrix is a rectangular array of numbers or other mathematical objects, for which operations such as addition and multiplication are defined. Most of this article focuses on real matrices, i.e., matrices whose elements are real numbers. For instance, this is a real matrix: The numbers, symbols or expressions in the matrix are called its entries or its elements. The horizontal and vertical ...
https://ronlevygroup.cst.temple.edu/courses/2016_fall/biost5312/lectures/biostat_lecture_02.pdf
The level of prostate-specific antigen (PSA) in the blood is frequently used as a screening test for prostate cancer. Assuming that each PSA+ and PSA− participant (or at least a representative sample of PSA+ and PSA− participants) is evaluated for the presence of prostate cancer. All PVs can be calculated from counting frequency directly.