In a simple mediation analysis I have a significant indirect effect, but no direct or total effect. I know some studies report this indirect effect as evidence of mediation, but from the examples I found it appears this exists for cases of suppression. From Kenny's website suppression exists if c' is the opposite sign to ab (and cites MacKinnon et al., 2007). However, in my analyses the c' (the direct effect) is the same sign to ab. When c' is positive ab is positive, and in another analysis when c' is negative ab is negative. Can I conclude mediation from this? If so, does anyone have examples of papers that do this? Thanks in advance!
The argument that there needs to be a significant direct effect in order to establish mediation was proposed by Baron and Kenny (1986) but has been shown to be false by Hayes (2013) – you can have significant mediation if the a and b paths are significant regardless of whether the c path is. Mermon et al (2018) suggest that if you have ab and c with opposite signs it is a situation called "competitive mediation".
Baron, R. M., & Kenny, D. A. (1986). The moderator-mediator variable distinction in social psychological research: Conceptual, strategic, and statistical considerations. Journal of Personality and Social Psychology, 51, 1173-1182.
Hayes, A. F. (2013). Introduction to mediation, moderation, and conditional process analysis: A regression-based approach. New York, NY: Guilford.
Memon, M. A., Cheah, J., Ramayah, T., Ting, H., & Chuah, F. (2018). Mediation Analysis Issues and Recommendations. Journal of Applied Structural Equation Modeling, 2(1), 1-9.
Dear Siobhán:
Both actions are complementary and independent each other. You can have a non-significant indirect effect and have a significant direct effect (which means there is not a mediation influence) or you can have a significant indirect effect and not a significant direct effect (which means X does not predict Y, but X predicts M and M predicts Y, which is a mediation). Obviously there are also cases in which direct and indirect effects are non-signiticant, or cases in which direct and indirect effects are both significant.
I put here some examples:
* Significant indirect effect and non significant direct effect: Galindo-Domínguez & Bezanilla (2021): Promoting Time Management and Self-Efficacy Through Digital Competence in University Students: A Mediational Model: https://www.cedtech.net/download/promoting-time-management-and-self-efficacy-through-digital-competence-in-university-students-a-9607.pdf
* Significant indirect effect and significant direct effect: Galindo-Domínguez et al. (2020): Mediator and moderator effect of resilience between self-efficacy andburnout amongst social and legal sciences faculty members. Article Mediator and moderator effect of resilience between self-eff...
Best regards.