identification problem

[gusl]

Can anyone explain the identification problem (very short article) in a non-confusing way?

Is this stuff used in the context of estimating supply separate from demand from time-series data? How can one separate these two if we can only measure one figure, namely sales?

I doubt there are any big conceptual hurdles here, but the presentation is confusing. Why do they use Q for both supply and demand?

Comments

[serapio.livejournal.com]

The two equations describe the two lines in the usual supply & demand X-shaped plot. In a two-dimensional model, you are just talking about prices as a function of quantities. Since the observables are the Q & P at the intersection of those lines, to estimate the $$a$$ and $$b$$ parameters you twiddle the X and Y variables, and collect data from how the system responds. I think. I'm not an economist.