Buy a certain Alt coin and then introduce some threat to Bitcoin and start shilling for a Alt coin..... The price of BTC goes down and the price of the Alt coins goes up. { depending on what coin is being shilled }
The only correlation that is CLEAR is that bitcoin has lost a TON of crypto market share in 2017. The reason is obvious - long confirmation times caused by a full blockchain and bloated mempool.
Several altcoins are showing promise technically as well. For example, Monero and Dash have better anonymity than Bitcoin. The markets have shown their support for this with higher prices. Bitcoin is going downhill technically - Segwit arguments against reality have been a waste of time and there is still no blocksize increase. The community deadlock has pushed the money elsewhere.