How to increase the vertical offset of exponent terms with increasing size of parentheses?

Question

I want to be able to write the following expression:

But have not been able to do so, since all I can get is:

I do not use the fraction of P/E, but rather just the psi. Can you help?

EDIT: After the suggestion of \left (and \right), I have managed to produce the following:

\begin{equation}
\hat{\psi}_{p,t}=n\displaystyle 
\left(\sum_{j=1}^{n}\big(\psi_{j,t})^{-1}\big)\right)^{-1}
\end{equation}

But it does not seem as if \big has an effect?

Answer 1

It's not entirely clear to me what you're trying to achieve in terms of sizing the inner and outer pairs of parentheses.

As far as I can tell, there is no need whatsoever to increase the size of the inner parentheses, if the term they enclose is \psi_{j,t}. For the outer parentheses, choose \biggl( and \right) -- using \left( and \right) would result in parentheses that are too tall, typographically speaking.

Here, then, is how I would rewrite your equation:

\documentclass{article}
\begin{document}
\[
\hat{\psi}_{p,t}=n\biggl( \sum_{j=1}^{n} (\psi_{j,t})^{-1} \biggr)^{\!-1}
\]
\end{document}