protocol in any way.

My setup is:

I have n animals.

I believe there is a linear relationship between x

(a covariate I can measure on each of the animals)

and the age of the animals.

Let's say I could measure both x and age with no measurement error at all.

I would still not expect the actual observations to lie on a perfect straight line

because 'life is messy', i.e. biological variation would still cause the individual

animal to deviate from the line.

Now, I am interested in predicting age. So my first instinct is to make a linear regression

of age on x, if for no other reason than that this will give me a line that minimizes deviaton

of age from the line.

However, I'm having problems interpreting my model. I mean, biological variation

can hardly count as a deviation in a single variable/in a single direction?

I feel like the 'noise term' should be some kind of two-dimensional thing.

I hope this question makes sense.

Cheers

Kettle.