# Why does LaTeX tell me that a { is missing?

Whenever I compile my document including the following code, it produces satisfactory output on the pdf, but gives me an error:

43
Missing { inserted.
<to be read again>
\gdef
l.43 \item $\mu_\hat{p}$ = mean of all possible values of $\hat{p} = \pi$. \\


\begin{itemize}
\item $\mu_\hat{p}$ = mean of all possible values of $\hat{p} = \pi$. \\
\item $\sigma_\hat{p}$ = standard deviation of all possible values of \^p =     $\sqrt{\frac{\pi(1-\pi)}{n}}$ \\
\item CLT (for \^p): If $n\pi \geq 10$ \underline{AND} $n(1-\pi) \geq to$, then the histogram of all possible values of \^p will be approximately normal. \\
\end{itemize}


What did I do wrong?

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Why are you mixing \^p with \hat{p}? It's the same symbol and it should be in the same shape every time. –  egreg Mar 13 '14 at 23:03
You need braces for the subscripts: \mu_{\hat{p}} and \sigma_{\hat{p}}. –  Gonzalo Medina Mar 13 '14 at 23:04
–  Peter Grill Mar 13 '14 at 23:08
Thanks! These are merely notes for a stats class that I typed in LaTeX as a way to try to learn the language, which explains my mixture of \^p with \hat{p}. –  dejongbrent Mar 15 '14 at 6:23

You need braces for the subscripts: \mu_{\hat{p}} and \sigma_{\hat{p}}

\documentclass{article}
\usepackage{amssymb}
\begin{document}

\begin{itemize}
\item $\mu_{\hat{p}}$ is the mean of all possible values of $\hat{p} = \pi$.
\item $\sigma_{\hat{p}}$ represents the  standard deviation of all possible values of $\hat{p} = \sqrt{\frac{\pi(1-\pi)}{n}}$
\item CLT (for $\hat{p}$): If $n\pi \geq 10$ \underline{AND} $n(1-\pi) \geq to$, then the histogram of all possible values of $\hat{p}$ will be approximately normal.
\end{itemize}

\end{document}


I also changed the text \^p to the math \hat{p} for consistency's sake, and suppressed the \\ at the end of each \item (those produce undefull \hboxes). Perhaps instead of $n(1-\pi) \geq to$ you meant something like $n(1-\pi) \geq t_{0}$?

Underlining it's not a nice typographical feature, so I would also suggest you to suppress it.

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Would you also remove the underlining? –  egreg Mar 13 '14 at 23:11
@egreg I added a recommendation to suppress it. –  Gonzalo Medina Mar 13 '14 at 23:13
I think it's supposed to say 10 instead of to. –  Mico Mar 13 '14 at 23:22
@Mico perhaps, but I am not sure, so I just left a comment suggesting to revisit that inequality. –  Gonzalo Medina Mar 13 '14 at 23:23
Thanks Gonzalo! And yes, that was supposed to say 10. oops. –  dejongbrent Mar 15 '14 at 6:24