Missing values

Frequently asked questions about PLS path modeling.
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johann
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Missing values

Post by johann »

How does smartpls treat missing values if you only define missing values in the data, but select not to treat the missing values with either mean replacement or case wise deletion.

Best regards
Johann
stefanbehrens
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Post by stefanbehrens »

It doesn't.

I.e. if you had your missings coded with say -999, SmartPLS would take these values for real and your results would obviously be very far off.

Good luck,
Stefan
johann
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Post by johann »

Thank you for your answer.

It would be good if Smartpls could do pair wise deletion. If you use mean replacement you will reduce varians in the data set. Which is not so good when using PLS. Case wise deletion will reduce your data to much if you don't have to many cases.

Best regards,
Johann
stefanbehrens
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Post by stefanbehrens »

I don't think smartPLS' algorithm would allow pair-wise deletion.
The only way this could work is to use pair-wise deletion in SPSS/ SAS to calculate a correlation/ covariance matrix. Then feed this matrix into Lohmoeller's LVPLS, which is also freely available on the web, to calculate your model.

A much better approach, however, has been suggested by C. Ringle in this forum. Simply do all your missing value treatments (listwise deletion, mean replacement, imputation, EM, etc.) in the statistical package of your choice BEFORE you load the data into SmartPLS. This way you have complete control over the process.

Cheers,
Stefan
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