Absolutely btc give big effect for altcoins, at the fact you can see and compare in the coinmarketcap that show the price of btc and most of altcoins. In my observation, when the price of btc increase it will effect to the price of most of altcoins which is increase too. And of the value of btc decrease it will effect to altcoins's price that will decrease too. Like today that btc just reach $6,313 per coin and eth decrease too that reach $191 per coin, so do to most of altcoins price that enter the red zone.