I just uploaded a new page on the “Stats Help” portion of my website. The link is here: Sobel Test Formula for Serial Mediation / Sequential Mediation .
In short, I spent much too long finding the sobel test formula for the indirect effect of X on Y through M1 and M2 in a serial mediation / sequential mediation. To prevent this from happening to other researchers (and possibly myself again), I provide a brief summary of mediation, sobel tests, and serial mediation / sequential mediation. Then, I provide the relevant sobel test formula.
If you want to know more about serial mediation / sequential mediation, please contact me at firstname.lastname@example.org. I’m always happy to chat about stats!