Regression line without intercept

Fig. 19. Work-function change A4>co after saturated CO adsorption at 300 K. A I>co vs. work function of corresponding clean surface area hkl. Symbols indicate terrace structure. Dashed line represents linear regression line, (a) Platinum. Intercept, Aq = 5.2 0.2 eV slope, Aj=-0.92 0.04 r = 0.997, without 210 and 320. (b) Rhodium. Intercept, Aq = 6.9 0.9 eV slope, Aj= -1.2 0.2 r = 0.97, without 430 and 321. From 90L. ...

The estimates of Intercept (b ) and slope (b ) are calculated so as to minimize the sum of squares (SS) of the deviations of the observed signals (y ) from the predicted value (y) at any concentration (x) without constraints. For some determinations, however, theory predicts that the response of the instrument should be linear with concentration and should also be zero when there is no analyte present. Thus, if the Instrument has been calibrated correctly, the calculated line should pass through the origin by definition. The proper regression model would then be the zero Intercept model shown as Equation 2. 

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