Correlation of Altcoins (incl ETH) and BTC?

[chr.rit]

Hi,

with the BTC going through the ceiling I have the feeling that all the other altcoins are under a severe pressure.

And somehow I explain this to my self like this:

the altcoin (e.g. an ETH token) is evaluated in an altcoin (ETH) which is basically evaluated on BTC.

Is there any mathematical correlation between these 3 layers or is just that everybody is leaving the tokens behind get more BTC?