How to fix the mismatch of font size of following?

Question

I want to generate the cases in the picture. However, the Symbols T₁, T₂ on LHS and RHS are different in size.

\documentclass[a4paper, 12pt]{report}
\usepackage[utf8]{inputenc}
\usepackage[showframe]{geometry}
\usepackage{mathtools]

\begin{document}

\mbox{}
$$
  (\mathcal{T}_{1},  \mathcal{T}_{2})=
   \begin{cases}
\frac{\left|\mathcal{T}_{1} \cap  \mathcal{T}_{2}\right|}{Min\ 
    {\left|\mathcal{T}_{1}\right|, \left|\mathcal{T}_{2}\right|\} } &  
       negative~test, \\
    -1 & positive~test 
    \end{cases}
$$
\end{document}

Answer 1

You can either set the \fraction using \displaystyle (via \dfrac), or use dcases. The latter provides a better solution since it results in better vertical spacing.

\documentclass{article}

\usepackage{mathtools}

\begin{document}

\[
  (\mathcal{T}_1, \mathcal{T}_2) = \begin{dcases}
    \frac{| \mathcal{T}_1 \cap \mathcal{T}_2 |}
      {\min\{| \mathcal{T}_1 |, | \mathcal{T}_2 |\}} &  
      \text{negative test}, \\
    -1 & \text{positive test}
  \end{dcases}
\]

\end{document}