In 41 patients, all hyperfunctioning parathyroid tissue was resected at the time of surgery and confirmed by a corresponding decrease in the intraoperative postexcision rapid PTH determination as well as by subsequent normalization of postoperative serum calcium and PTH levels and resolution of clinical symptoms.
In other words, the standard deviation Ï (sigma) is the square root of the variance of X; i.e., it is the square root of the average value of (X â Î¼) 2. The standard deviation of a (univariate) probability distribution is the same as that of a random variable having that distribution.
It turns out that in a simple regression model, the fraction of variance explained is precisely the square of the correlation coefficient--i.e., the square of r. Hence, the fraction-of-variance-explained has come to be known as R-squared. The interpretation and use of R-squared are discussed in more detail here.