I use this map to discuss how to verify a source (spoiler: I love the map, and the data on it looks OK to me.) During the talk I often joke that this confirms something that, as a hard rock fan, I already guessed: overall, the less sunlight a country gets, the more metal bands it tends to have.
The audience loves this joke, but is it true? It turns out that, at least at a first glance, it may not be or, at least, it needs some caveats. Here's a quick ggplot2 of the relationship between the average yearly sunshine duration in the capitals of most of these countries and the concentration of metal bands (Note: I used the capital as a rough proxy, being very aware that many of these countries are big, so that the amount of sunlight within them varies a lot. In Spain, for instance, the South is very sunny, but Northern regions such as Galicia, where I was born, are cloudy, rainy, dark —and maybe very metal):
If we isolate the first group, with the exception of an outlier (Iceland) the relationship is positive: the more sunlight, the more metal bands. And if we ignore the four outliers on the Y-axis from the overall mix (Finland, Norway, Sweden, and Iceland,) there's barely any relationship. See graphs below.
What can we learn from all this? Not much, I guess, other than that even silly jokes ought to be verified and presented with plenty of caveats.