# Thread: Multiple Regression Analysis - Two independent variables, one w/same values

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2. ## Re: Multiple Regression Analysis - Two independent variables, one w/same values

Conceptually you can't estimate the effect of a variable if it isn't... a variable. More concretely the intercept term and the "slope" for X1 cannot be uniquely identified from the data because they're perfectly collinear.

3. ## Re: Multiple Regression Analysis - Two independent variables, one w/same values

An interesting starting point for you for you to mull over. Effectively if you run OLS and want an estimate of the intercept, that's exactly what you have. The data matrix has x_0 with all the values = 1.

4. ## Re: Multiple Regression Analysis - Two independent variables, one w/same values

From perspective of G-M assumptions, this is likely to violate the collinearity assumption. Here is an amazing read for anyone looking into OLS assumptions: Berry, W. D. (1993). Understanding regression assumptions (Vol. 92). Sage Publications.

5. ## Re: Multiple Regression Analysis - Two independent variables, one w/same values

ablong,

Is your issue just that your sample is too small to represent the true variability of the population of interest?

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