# Model Formula with deflator

I'm having difficulties to find the right model formula for my model:

$Y_i=a+bX_i$ where Y and X are both deflated by another variable

y1/def ~ x1/def + x2/def


returns a model with interactions. How can i prevent R from doing so?

• Did this help you get the desired behavior? Jul 29, 2014 at 6:48
• As a word of caution, be careful with dividing by def, however--if it's a random variable then dividing both sides by def could completely change the functional form of your regression. Just throwing that out there... Jul 29, 2014 at 7:36
• Thank you for your answer and the hints on deflating. I wasnt able to check yet. Will comment when I did so. Jul 29, 2014 at 14:52

If you want to perform a transformation on the variables in the regression, you'll have to use the I() function:
I(y1/def) ~ I(x1/def) + I(x2/def)

Basically, you use the I() function in a formula whenever you want an expression to be treated "as is". For example, if you have a data frame with three columns, a, b, & c, and you want to regress c onto the sum of columns a and b you would write: c ~ I(a + b) since--as you've seen yourself--entering: c ~ a + b would give you a totally different regression.