Sunday, April 1, 2007

Don't standardize the parameters

If you are doing a linear regression, it is recommended that you interpret unstandardized coefficients (betas) rather than standardized ones (Mendenhall, Sincich, 2003). By standardizing the coefficients, you are losing the weights of independent variables on the dependent variable. Also, you are trying to compare non-comparable variables.

For example, let's say that you have two independent variables "age" and "education" (both in years) explaining a dependent variable, say, salary. If betas associated with the two dependent variables are 1,000 and 10,000 respectively, you interpret the betas as follows:

One unit of increase in age increases the salary by 1,000 units, keeping education constant. Similarly, one unit of increase in education increases the salary by 10,000 units, keeping age constant.

As seen in this example, one unit of education is more influential on salary than age. If you standardize the coefficients, you may lose this information. Furthermore, standardization makes one unit of age equal to one unit of education. However, one unit of age is never equal to one unit of education.

That is why some of the statistical software packages like SAS do not report standardized betas in their output...

Mendenhall, W., Sincich, T., "A Second Course in Statistics: Regression Analysis", 6th ed. Upper Saddle River, N.J.: Prentice Hall, 2003.
ISBN-10: 0130223239

Thursday, March 29, 2007

Why tractable USB drives are dangerous!

I bought a tractable 1 GB USB drive from LG nearly a year ago, and guess what: it died right after the warranty expired. However, I am not sure if LG would be replacing the drive if the warranty didn't expire. Because it is very easy for electronics companies to blame the consumer when there is a malfunction. It is likely that it is you who misused or abused the product.

Anyway, one of the reasons why this drive failed is because it was tractable. If the device is made up of movable parts, there is a high probability that one day it is going to either stop moving, or break into half from where it moves...

Now I have a 2 GB intractable Memorex drive with the expense of using a cap all the times... I'll be writing my impression about this drive shortly...