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I want to have the | the correct size for the situation and since I can't use \left and \right, I tried to use \large but it didn't change. Help?

\[ I(\theta)=-\E\left\lbrace\frac{d^2\ln{\left[f(X|\theta)\right]}}{d\theta^2}|\theta\right\rbrace\]
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While code snippets are useful in explanations, it is always best to compose a fully compilable MWE that illustrates the problem including the \documentclass and the appropriate packages so that those trying to help don't have to recreate it. – Peter Grill Mar 28 '13 at 22:25
\large really only affects text. for delimiters, there are \big, \Big, \bigg. and \Bigg` that are nondirectional, and also \bigl, \bigr, etc., to indicate left or right versions. – barbara beeton Mar 28 '13 at 22:26
Thanks for the MWE! Please always make sure to remove all packages that don’t seem to have any influence on the problem; see my answer at I've just been asked to write a minimal example, what is that?. – doncherry Mar 28 '13 at 23:43
up vote 4 down vote accepted

There's no reason for using \left and \right in the inner formula. I would also omit the square brackets. For the big bar, use \;\middle|\;. For the inner bar, \mid provides a good spacing.

  \frac{d^2\ln f(X\mid\theta)}{d\theta^2}

enter image description here

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Out of curiosity, what's the difference between \left\lbrace and \left\{? – Jubobs Mar 28 '13 at 22:36
@Jubobs The number of characters needed. :) – egreg Mar 28 '13 at 22:40
Thanks! And I understand about the inner left and right and getting rid of the square brackets, they're there to keep with the format of the rest of the document, there are brackets strictly defining the subject of each ln, sin, cos etc... – DannyBland Mar 28 '13 at 23:27
@DannyBland Mathematica writes Sin[x], mathematicians don't. :) – egreg Mar 28 '13 at 23:28

You should use \lvert and \rvert for | as in $\lvert x \rvert$, or \mid as in $a \mid b$. Those give the right spacing.

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This doesn't seem to address the problem. – egreg Mar 28 '13 at 23:26
@egreg It does if you replace the \mid by \mid|. – DannyBland Mar 28 '13 at 23:28

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