Bitcoin has more dominance and popularity in the crypto market and that affects every other coins in the market. When the price of bitcoin goes high, ETH and other coins will have the strength to reach new price heights, but when the price of bitcoin drops, so goes all altcoins.
For ETH and BTC, the margins depends on how hard it goes, either up or down. The harder the price of BTC goes down, so doe ETH, but when the price of BTC goes up, and the have a little correction, it doesn't affect ETH.