Dear Marco, thank you! Yes I think selection bias is quite strong. History is tough to quantify. The deeper in past the harder it is to detect fabrication and access cultural background, so the perception is distorted. On the other hand, perception of modern history is strongly distorted by politics and mass media. My old highschool history teacher was suggesting that history is akin quantum mechanics: one can make only probable descriptions and one's "measurements" (journalism) might affect the outcome and you always part of the process. This challenges make it even more interesting though.