dot-Rbar2: Adjusted R-squared \bar{R}^{2} (from R^2)
In jeksterslabds/jeksterslabRlinreg: Jekster's Lab Linear Regression Utilities

Calculates the adjusted coefficient of determination

\bar{R}^{2} = 1 - ≤ft(\frac{RSS / ≤ft( n - k \right)} {TSS / ≤ft( n - 1 \right)} \right) = 1 - ≤ft( 1 - R^2 \right) \frac{n - 1}{n - k} .

1	.Rbar2(R2 = NULL, n, k, X, y, fromRSS = TRUE)

`R2`	Numeric. Coefficient of determination R^2 .
`n`	Integer. Sample size.
`k`	Integer. Number of regressors including a regressor whose value is 1 for each observation.
`X`	`n` by `k` numeric matrix. The data matrix \mathbf{X} (also known as design matrix, model matrix or regressor matrix) is an n \times k matrix of n observations of k regressors, which includes a regressor whose value is 1 for each observation on the first column.
`y`	Numeric vector of length `n` or `n` by `1` matrix. The vector \mathbf{y} is an n \times 1 vector of observations on the regressand variable.
`fromRSS`	Logical. If `TRUE`, calculates the coefficient of determination from `RSS`. If `FALSE`, calculates the coefficient of determination from `ESS`.