How strongly related is altcoin value to bitcoin price?
It is strongly correlated from what you see in the data trends. Let’s explain the basics then throw some examples.

Simple math, ALT/BTC ratio would decrease if:
- ALT coin’s value drops (i.e. people are selling the ALT coin or trading it for BTC or other ALT coins).
and/or
- BTC value increases (i.e., more demand for BTC from various accounts including USD and ALT coin conversion)

Similarly, ALT/BTC ratio would increase if:
- ALT coin’s value increases (i.e. people are buying an ALT coin by trading BTC or other ALT coins).
and/or
- BTC value decreases (i.e., BTC is cashed out for USD or other currency or traded for ALT coins)