Hi there,

I calculated a multiple regression with unstandardized data using lm and got those values:

```
Call:
lm(formula = reg.modeldef2d, data = dta2)
Residuals:
Min 1Q Median 3Q Max
-1.48129 -0.47499 -0.03837 0.43007 1.32839
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) -1.96183 0.68485 -2.865 0.00535 **
WPR.Teiler.theta 0.11308 0.13375 0.845 0.40041
WPR.Prim.theta -0.16453 0.09212 -1.786 0.07794 .
SD.math 0.38957 0.13936 2.795 0.00650 **
SR3.theta 0.20984 0.10707 1.960 0.05355 .
SW2.Teiler.theta 0.05043 0.09504 0.531 0.59716
SR3.theta:SW2.Teiler.theta 0.22049 0.08912 2.474 0.01550 *
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 0.6724 on 79 degrees of freedom
Multiple R-squared: 0.4074, Adjusted R-squared: 0.3624
F-statistic: 9.052 on 6 and 79 DF, p-value: 1.583e-07
```

Then I standardized the data using scale() and calculated the very same regression:

```
Call:
lm(formula = reg.modeldef2d, data = dta2_std)
Residuals:
Min 1Q Median 3Q Max
-1.75916 -0.56409 -0.04557 0.51075 1.57757
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) -0.02616 0.08675 -0.302 0.7638
WPR.Teiler.theta 0.08763 0.10365 0.845 0.4004
WPR.Prim.theta -0.17215 0.09639 -1.786 0.0779 .
SD.math 0.36673 0.13119 2.795 0.0065 **
SR3.theta 0.23590 0.11639 2.027 0.0461 *
SW2.Teiler.theta 0.05409 0.10077 0.537 0.5930
SR3.theta:SW2.Teiler.theta 0.21524 0.08700 2.474 0.0155 *
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 0.7985 on 79 degrees of freedom
Multiple R-squared: 0.4074, Adjusted R-squared: 0.3624
F-statistic: 9.052 on 6 and 79 DF, p-value: 1.583e-07
```

The p-values are not the same! Also, the intercept isn't at 0 (which it should with standardized data, shouldn't it?)

I checked for NA-values, but none exist.

Is it possible that the accuracy of the R variables is the problem? When rescale the standardized data manually and calculate the differences to the original unstandardized values, not all differences are zero (but small numbers, like E-17).

It's kind of a problem because after the standardization the factor SR3.theta suddenly gets significant...

Thanks for all your help in advance!

Regards, Martin