Covariances and parameter confidence intervals from light-element R-matrix evaluations.

R-matrix parameter covariances for light elements with A 16 are calculated within the Wigner-Eisenbud multichannel unitary R-matrix theory. We review the theoretical foundation, numerical approach, and determination of the parameter covariances within this approach. We derive the relation between the parameter variance, as the diagonal elements of the covariance matrix, and the parameter confidence interval based upon the chi-squared distribution. Cross section covariances computed from the parameter confidence intervals are calculated for several compound systems and discussed. [ABSTRACT FROM AUTHOR]