Align \overline in equation

Question

I'm quite new to LaTeX and struggling with the alignment in math mode. Is there any way to nicely align the bar in my equation:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

We denote by
\begin{equation}
    \text{OOB-MSE} = \frac{1}{n}\sum_{i=1}^{n}(y_i - \bar{\widehat{y}}_{i \: \text{OOB}})^2,
\end{equation}
the so-called out-of-bag mean square error, where $\overline{\widehat{y}}_{i \: \text{OOB}}$ is the averaged... 

\end{document}

I also tried the command from another similar question (Aligning issue with overline) but it's much smaller than the overline bar and still not really aligned..

\newcommand{\myol}[2][3]{{}\mkern#1mu\overline{\mkern-#1mu#2}}

Thanks!

The first bar in the picture uses the \bar command and the second uses the \overline command. Both aren't nicely aligned.

Answer 1

Here I write my proposal using accents package. I have used this trick

\accentset{\mkern2.55mu\_}{\widehat{y}}

to have the bar and centering the widehat. Of course you can create a macro, but the advice that if you change the letter y for example you must change the value of \mkern2.55mu.

\documentclass[12pt]{article}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{accents}
\begin{document}

We denote by
\begin{equation}
    \textup{OOB-MSE} = \frac{1}{n}\sum_{i=1}^{n}(y_i - \accentset{\mkern2.55mu\_}{\widehat{y}}_{i \: \textup{OOB}})^2,
\end{equation}
the so-called out-of-bag mean square error, where $\accentset{\mkern2.55mu\_}{\widehat{y}}_{i \: \textup{OOB}}$ is the averaged... 

\end{document}