Should there be an "i" in a regression equation? I have developed a general linear model to predict my dependent variable Y. I am unsure on how to present my equation.
Should it be: (not sure if the i should be there or not)
$Yi= .432 + .320 Age_i + .520 WE_i + .300 JP1_i + .210 JP2_i$
or
$Y= .432 + .320 Age + .520 WE + .300 JP1 + .210 JP2$
Where:
WE= work experience;
JP= Job Position;
JP1= floor level staff;
JP2= Managers;
 A: The $i$'s usually index the observations in the sample used to fit the model, so if you simply want to present the predictive equation for a single new observation, there's no need for them. Also be careful not to confuse the random variable, its observed values, & the fitted values: if you've previously defined $Y_i$ as the $i$th observed value of the dependent variable then
$$Y_i= .432 + .320 Age_i + .520 WE_i + .300 JP1_i + .210 JP2_i$$
is wrong because it omits the residual term. A common notational scheme is $Y$ for the random variable, $y$ for its observed values, & $\hat{y}$ for the fits.
I'd suggest you write the equation like this
$$\hat y = 0.432 + 0.320  x_1 + 0.520 x_2 + 0.300 x_3 + 0.210 x_4$$
(defining the terms appropriately) or like this 
$$\mathrm{Salary} = 0.432 + (0.320  \times \mathrm{Age}) + (0.520 \times \mathrm{WE}) + (0.300 \times \mathrm{JP1}) + (0.210 \times \mathrm{JP2})$$
rather than mixing up formal mathematical notation with a word equation. NB:


*

*Italics emphasize single-letter place-holders for numbers, functions, or operators that you define. Don't use them in word equations. (In any case, in the LaTeX math environment fluff gives the product $fluff$; \mathit{fluff} gives the italicized word $\mathit{fluff}$.)

*S.I. (& I'd wager any other convention written down as such) mandates showing leading zeroes before decimal points.

*The brackets in the word equation aren't necessary, but your readers may not know that.

*With many terms a table of coefficients is more convenient.
A: Both are correct, but if you use the i 's they should preferably be subscripts:
$Y_i = .432 + .320Age_i + .520WE_i + .300JP1_i + .210JP2_i$
If you don't use the i's then the equation is about vectors. 
