You could do a study with a lot more data points than that to see if there's a correlation. Which someone has, and there is: "Overall the results of the paper suggest that policies that enhance labor market flexibility
should reduce unemployment."
It wasn't a study, but showing that you can have the strongest labor protections and negligible unemployment. Worth striving for. But there are actual studies, including a few citing yours, that show no such relation. Regardless, a 1.29 point increase in unemployment for not having at-will employment sounds like a bargain to me.
https://www.imf.org/external/pubs/ft/wp/2012/wp1264.pdf