# Synthetic Control Method difference between MSPE and RMSPE

I am using Synthetic Control Method to estimate the effect some policy had. Got results and everything but when started to discuss inference method and placebo tests I have hit the wall. I got the $$\frac{\mathrm{Post \; MSPE}}{\mathrm{Pre \; MSPE}}$$ ratio from Synth() package, which I believed to be equal to p-value (at least that's what R reported). Yet, on numerous pages across the Internet I have found the information that the p-value is in fact equal to $$\frac{\mathrm{Post \; RMSPE}}{\mathrm{Pre \; RMSPE}}$$. Pretty sure, Synth() does not produce the aforementioned ratio - but then again, which one should I use?

Abadie et al. (2010) talks about MSPE - then 5 years later, Abadie et al. (2015) starts using RMSPE. I find it a little bit confusing and would really appreciate if someone could explain it to me.