When I hover over the "Preparedness Center" in the available projects list on a planet, I see the description "Boost Planetary Defence...". However, the bonus it provides is supposedly "Resistance +25%".
Please correct me if I'm wrong, but I think "Planetary Defence" (applies when planet is invaded) is different from "Resistance" (resistance to culture flipping).
Edit: From the planet where I built this, it increases Resistance +25%, so the description is incorrect.