Principal Components

Eigenanalysis - Eigenvalues

  

Use the eigenvalue results to determine the number of principal components.

One way to determine the number of principal components is based on the size of eigenvalues. In the eigenanalysis of the correlation matrix, the eigenvalues of the correlation matrix equal the variances of the principal components. According to the Kaiser criterion, retain principal components with eigenvalues greater than 1.

You can also decide on the number of principal components based on the amount of explained variance. For example, you may retain components that cumulatively explain 90% of the variance. Another technique is to analyze a scree plot. Use any one or combination of these techniques to determine the number of principal components.

Example Output

Eigenanalysis of the Correlation Matrix

 

Eigenvalue    3.5476    2.1320    1.0447    0.5315    0.4112

Proportion     0.443     0.266     0.131     0.066     0.051

Cumulative     0.443     0.710     0.841     0.907     0.958

 

Eigenvalue    0.1665    0.1254    0.0411

Proportion     0.021     0.016     0.005

Cumulative     0.979     0.995     1.000

Interpretation

For the loan applicant data:

·    The first principal component has variance 3.5476 (equal to the largest eigenvalue) and accounts for 0.443 (44.3%) of the total variation in the data.

·    The second principal component (variance 2.1320) accounts for 0.266 (26.6%) of the total data variation.

·    The third principal component (variance 1.0447) accounts for 0.131 (13.1%) of the total data variation.

The first three principal components with variances equal to the eigenvalues greater than 1 represent 0.841 (84.1%) of the total variability, suggesting that 3 principal components adequately explain the variation in the data.

 


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