Interesting. Though as mentioned the ratings of shows are largely skewed by time -- ie: because no one was reviewing shows from the 50s-80s at the time of airing, it's all viewed through nostalgia and history, so it skews to certain shows and avoids even reviewing the dreck.

When you get into the 90s and beyond, shows were being viewed and reviewed contemporaneously and therefore everything was covered and a greater range was covered so overall ratings for the period actually went down...

Nice analysis of the available data anyway. Also interesting to see the appearance of certain non-English language shows as well.