I think to some extent the entire crypto market is correlated. I mean there are some people that refuse to use certain cryptos/blockchain and some enthusiasts of different cryptos however if you have dipped into one crypto currency you will likely have your hands in other cookie jars.
And well, if one of the big ones is doing well then the rest tend to follow as people are more likely to buy crypto on bullish trends but when one starts to crash people will sell out of all of them in fear of them following and as such case it to crash.
This is my hypothesis, may not be right but this can also explain why steem and etherium have a stronger correlation as so many people cam to steem through etherium and when I joined steem a very big chunk of the cryptocurrency posts were etherium meaning we have a very big etherium community on the steem blockchain.
My hypothesis of the situation.
RE: Some relations among various cryptos