# When do improper linear models get robustly beautiful?

Are improper linear models used in practice or are they some kind of curiosity described from time to time in scientific journals? If so, in what areas are they used? When would they be useful?

They are based on linear regression

$$y=a+b∑iwixi+ε y = a + b \sum_i w_i x_i + \varepsilon$$

but $$wjw_j$$‘s are not coefficients estimated in the model, but are

• equal for each variable $$wi=1w_i = 1$$ (unit-weighted regression),
• based on correlations $$wi=ρ(y,xi)w_i = \rho(y, x_i)$$ (Dana and Dawes, 2004),
• chosen randomly (Dawes, 1979),
• $$−1-1$$ for variables negatively related to $$yy$$, $$11$$ for variables positively related to $$yy$$ (Wainer, 1976).

I also saw features being $$zz$$-scaled and the output being weighted using simple linear regression

$$y=a+bv+ε y = a + b v + \varepsilon$$

where $$v=∑wixv = \sum w_i x$$, and can be simply estimated using OLS regression.

References:
Dawes, Robyn M. (1979). The robust beauty of improper linear models in decision making. American Psychologist, 34, 571-582.

Graefe, A. (2015). Improving forecasts using equally weighted predictors. Journal of Business Research, 68(8), 1792-1799.

Wainer, Howard (1976). Estimating coefficients in linear models: It don’t make no nevermind. Psychological Bulletin 83(2), 213.

Dana, J. and Dawes, R.M. (2004). The Superiority of Simple Alternatives to Regression for Social Science Predictions. Journal of Educational and Behavioral Statistics, 29(3), 317-331.

This gains in robustness over an ordinary MLR procedure because the number of parameters ($\downarrow$df) is reduced, and introduces inaccuracy because of augmented omitted variable bias, OVB. Because of the OVB, the slope is flattened, $|\hat\beta|<|\beta|$, the coefficient of determination is reduced $\hat{R}^2.