Negative or Net suppression/reciprocal or cooperativa suppression in mediated or PLS- SEM models

The negative sign in the path  or weight means “negative or net suppression”. This is a common issue when using several variables correlated in the same model. The tricky issue is that all variables are positively related wth SC-Ad (se latent variable correlations in 2nd order HOC model), but you can observe a negative value in the path. How can this be possible? It is well documented in mediation analysis (i.e., Ato & Vallejo, 2011 page 558), and it is explained by the relative “impact” of the predictors on the dependent variable. The predictor less correlated with the dependent variable is used to “compensate” the “inflate” paths for the other predictors. The negative or net suppression occurs when all the variables have a high positive correlation among themselves (rXY, rXZ, rZY > 0), but the regression coefficient of one of the variables is negative. Reciprocal or cooperative suppression occurs when two variables are negatively correlated with each other, but both are positively correlated with the outcome variable.

Inconsistent Mediation (from Mediation (David A. Kenny) (davidakenny.net))

"If c' were opposite in sign to ab something that MacKinnon, Fairchild, and Fritz (2007) refer to as inconsistent mediation, then it could be the case that Step 1 would not be met, but there is still mediation. In this case the mediator acts like a suppressor variable. One example of inconsistent mediation is the relationship between stress and mood as mediated by coping. Presumably, the direct effect is negative: more stress, the worse the mood. However, likely the effect of stress on coping is positive (more stress, more coping) and the effect of coping on mood is positive (more coping, better mood), making the indirect effect positive. The total effect of stress on mood then is likely to be very small because the direct and indirect effects will tend to cancel each other out. Note too that with inconsistent mediation that typically the direct effect is even larger than the total effect."

  

Ato, M., & Vallejo, G. (2011). Los efectos de terceras variables en la investigación psicológica. Anales de Psicología, 27(2), 550-561. http://digitum.um.es/jspui/handle/10201/26561

 

Conger, A. J. (2016). A Revised Definition for Suppressor Variables: a Guide To Their Identification and Interpretation. Educational and Psychological Measurement, 34(1), 35-46. https://doi.org/10.1177/001316447403400105
Gaylord-Harden, N. K., Cunningham, J. A., Holmbeck, G. N., & Grant, K. E. (2010). Suppressor effects in coping research with African American adolescents from low-income communities. J Consult Clin Psychol, 78(6), 843-855. https://doi.org/10.1037/a0020063
Krus, D. J., & Wilkinson, S. M. (1986). Demonstration of properties of a suppressor variable. Behavior Research Methods, Instruments, & Computers, 18(1), 21-24. https://doi.org/10.3758/BF03200988
MacKinnon, D. P., Krull, J. L., & Lockwood, C. M. (2000). Equivalence of the Mediation, Confounding and Suppression Effect. Prevention Science, 1(4), 173-181. https://doi.org/10.1023/A:1026595011371

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Mi primer día en serio con R statistical package

Tras varios años tonteando con la posibilidad, hoy es el primer día que me tomo en serio aprender a usar R (http://en.wikipedia.org/wiki/R_%28programming_language%29).  ¿Por qué empezar con R si dicen que es complicado familiarizarse con él y yo me manejo muy bien con las sintaxis de SPSS y EQS?

Hay varios motivos. En primer lugar, no se trata de migrar a R. Probablemente seguiré con SPSS y EQS para mi trabajo científico. Sin embargo necesito un software libre para poder usar en los cursos de formación que imparto (que no obligue a los alumnos a pagar una licencia cara si quieren aplicar en el futuro lo que aprendan) y, sobre todo, para que mis alumnos de grado, cuando vayan a trabajar a las empresas (que jamás tendrán licencia de programas como SPSS o EQS), puedan seguir usando la estadística como apoyo para sus decisiones. Además, es probable que tenga que usar este soft con mis alumnos de doctorado (por los mismos motivos). El día que eso pase supongo que se habrá iniciado un proceso de migración en el que R se convierta en el programa básico para mi trabajo. De momento sólo opta a ser el acompañante minoritario.

Os dejo un enlace donde hacen una breve introducción al programa:

http://www.highstat.com/BGRCourse/Sections11TO14V2.swf

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