Correct enunciation of $ \, \sum \big( {Y_{i}}-{ \hat{Y}_{i}} \big)^2$ How can I enunciate this notation correctly, could you show me that, please?
$$ \sum \big( {Y_{i}}-{ \hat{Y}_{i}}  \big)^2 $$
Thank you very much.
 A: It sounds like you are looking to learn how to pronounce the expression.
If you were going to speak fairly literally you could say

The sum of WHY EYE minus WHY HAT EYE squared

or 

The sum of the quantity WHY EYE minus WHY HAT EYE, squared

However, when speaking to formulas it is common to get a little more abstract. And in such a formula $Y$ would typically refer to the variable being modelled and $\hat{Y}$ would refer to your prediction. Thus you could say things like:

The sum of squared residuals

or 

the sum of squared differences between observed Y and predicted Y.

and presumably many other things.
I compiled a list of mathematical pronunciation guides which you may find useful. In particular, you might want to have a look at this one by H. VÄaliaho.
A: It is referred to as the sum of squared deviations from the means.  As Macro writes it can also be called the residual sum of squares when you view $\hat{Y}_i$ as model mean for the $i$'th observation and then $Y_i-\hat{Y}_i$ is the model residual for observation $i$.  
