# Thread: Principle Components Analysis and Cluster Analysis

1. ## Principle Components Analysis and Cluster Analysis

Hi,

I was wondering if you could all hep me decode the difference between both PCA and cluster analysis. As far as I can tell, PCA aims toreduc/cluster the variables, but cluster analysis attempts to cluster the results?

Thanks

QOS

2. ## Re: Principle Components Analysis and Cluster Analysis

Principle Components Analysis (PCA) and Factor Analysis are data reduction techniques. The objective to to reduce large numbers of variables to a smaller number of "factors", or underlying constructs that explain the variation. For example, you have data on gripping strength of each hand, lower and upper arm strength. You have the same for different measures of leg strength. PCA or Factor Analysis might reduce this to two constructs called upper body strength and lower body strength. Both methods focus on the Independent Variables.

Cluster Analysis may be run on raw data, scores from Factor Analysis, or on variables. For the first two, CA will find clusters of entities (think market segments) that behave in a similar fashion. For the latter, CA will find variables that measure similar responses. This is particularly useful to identify survey questions that are asking the same thing.

3. ## The Following User Says Thank You to Miner For This Useful Post:

QueenOfStats (05-07-2013)

4. ## Re: Principle Components Analysis and Cluster Analysis

Another way of understanding is that PCA factors the variables whereas Clustering works on rows of data.

5. ## The Following User Says Thank You to chetan.apa For This Useful Post:

QueenOfStats (05-07-2013)

6. ## Re: Principle Components Analysis and Cluster Analysis

Perfect, thanks for the help!
So they're quite similar then, I guess, but can both approach things with a different angle. Cluster analysis isn't really reducing data, but just finding a way to capture the scores. But PCA is reducing the variables rather than the outcomes, right? This **** is intense

7. ## Re: Principle Components Analysis and Cluster Analysis

Originally Posted by QueenOfStats
But PCA is reducing the variables rather than the outcomes, right?
That is correct.

8. ## The Following User Says Thank You to Miner For This Useful Post:

QueenOfStats (05-07-2013)

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