Finally, we used tetrachoric correlations to estimate the A (additive genetics), the C (shared environmental) and the E (non-shared environmental) components based on the following definitions:\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$r_{MZ} = {{{\mathrm{A + C}}}}$$\end{document}rMZ=A + C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$r_{DZ} = 0.5{{{\mathrm{A}}}} + {{{\mathrm{C}}}}$$\end{document}rDZ=0.5A+C\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$var = {{{\mathrm{A}}}} + {{{\mathrm{C}}}} + {{{\mathrm{E}}}}$$\end{document}var=A+C+E
