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PLS Junior User
Posts: 8
Joined: Thu Jul 26, 2018 1:33 pm
Real name and title: tinker


Post by tinker18 » Sun Aug 12, 2018 12:10 pm

Hello everyone,

I have three mediators in my model; Two of it are partial mediation and 1 full mediation. The full mediation shows a VAF value of 1.075 which is above 100%. I know that VAF is not required for full mediation but I'd like to know if I am calculating it correctly?

A= Independent variable, B = dependent variable, M = mediator.

A to M = 0.552
M to C = 0.469
A to B= -0.018

0.552 x 0.469 / (0.552 x 0.469 + (-0.018)) = 1.075%

However, according to a friend, we need to consider only the absolute value and disregard the negative sign. That is,
0.552 x 0.469 / (0.552 x 0.469 + 0.018) = 93.49%.

May I know which calculation is correct?

Thank you.

SmartPLS Developer
Posts: 971
Joined: Tue Mar 28, 2006 11:09 am
Real name and title: Dr. Jan-Michael Becker


Post by jmbecker » Sun Aug 12, 2018 2:30 pm

Your calculations seem to be generally correct. However, a problem with the VAF is that it does not work with negative effects (indirect or direct). Some people propose to only use the absolute effects to circumvent these problems, but the main question is: what do you want to measure with the VAF and why?
Dr. Jan-Michael Becker, University of Cologne, SmartPLS Developer
Researchgate: ... v=hdr_xprf
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