Problem with tipa \textnrleg

Question

The expected "long leg n" turns out as "6".how come the words after the long leg n will appear in next line? {where l is the log likelihood function,\\ \mathnrleg is the vector of nuisance parameters,\\ ($\hat{\theta}$,$\hat{\mathnrleg}$) is the maximum likelihood estimator of($\theta$,$\mathnrleg$),\\ $\tilde{\mathnrleg}$ is the restricted maximum likelihood estimator of $\mathnrleg$ under $\text {H}_0.$}

MWE:

\documentclass[12pt]{beamer}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage[T1]{tipa}
\usepackage{tipx}
\usetheme{Frankfurt}
\usefonttheme{serif}
\usecolortheme{dolphin}

\begin{document}
\begin{frame}

\textcolor{blue}{\underline {Likelihood Ratio Method}}
\begin{itemize}
\item For a scalar parameter of interest $\theta$, the likelihood ratio statistic for testing the null hypothesis, $\text{H}_0$: $\theta$= $\theta_0$ versus $\text{H}_1$: $\theta$ $\neq$ $\theta_0$ is given as,
\setlength{\abovedisplayskip}{0pt}
\setlength{\belowdisplayskip}{0pt} 
$$\Psi=2[l(\hat{\theta},\hat{\textipa{\textnrleg}}$$
\end{itemize}
\end{frame}
\end{document}

Answer 1

If your aim is to use the “long tailed n” as a math symbol, define a command for it. Since \textnrleg is supposed to appear in text, add \textnormal around it. Using \text is not sufficient, because the tipx font lacks other shapes and you'd get again a 6 if you use just \text{\textnrleg} in an italic or boldface context.

I minimized the code, as beamer is not necessary.

\documentclass{article}
\usepackage{amsmath}
\usepackage[T1]{tipa}
\usepackage{tipx}

\newcommand{\mathnrleg}{\textnormal{\textnrleg}}

\begin{document}
\[
\Psi=2[l(\hat{\theta},\hat{\mathnrleg}
\]
\end{document}

Don't use, under any circumstances, $$ in a LaTeX document.