PCA

Hi!

I used your pca.xls file in order to calculate the scores for each component. I used your equation:

PC1 = 0.207 WDIM + 0.873 CIRCUM + 0.261 FBEYE + 0.326 EYEHD  + 0.066 EARHD + 0.128 JAW
PC2 = -0.142 WDIM -0.219 CIRCUM - 0.231 FBEYE + 0.891 EYEHB + 0.222 EARHD - 0.187 JAW
But I did not get the same scores as yours.

Could you tell me in this exercise what I must to input in WDIM, FBEYE, EARHD and JAW. I know that those names are for the variables, but does it means the standardized values for each variable?
Many thanks!
Mercedes

Comments

  • Hi Mercedes

    Yes, to calculate the correct scores you simply have to standardise the raw values for the variables before entering them into the equation. When working with a PCA based on a correlation matrix you simply standardise the raw values so that each variable has a mean of 0 and then enter them into the equations that you've shown above.

    Hope this helps

    Alan
  • Hi Alan,

    Thank you for replying my message. About this example, I standardized the values as follows:

    xi - mean x for the ith variable]/standard deviation

    If I use this equation I do not get the PC scores that you showed in your example:
    PC1= 2.1705
    2.6172
    2.2271 and so on.

    Instead of doing this, I just remove the mean and I got the same PCA scores that you showed in your example for doing PCA.
    So, Why did you mention the equation (above) in your example for doing PCA?
    Thank you!!
    Mercedes
    Ps. I did everything step by step in Excel, if you're interested I can send it right away.

Sign In or Register to comment.