If you are talking about fiat price, altcoins generally follow bitcoin, but at a much slower rate when going up and a faster rate going down. If you are talking about alts v btc pairings, when bitcoin is moving up hard, alts generally go down or move sideways, when bitcoin is dumping, alts dump harder, when bitcoin is moving sideways, the altcoins market shines. There are always exceptions to the rule, but not many. Think of bitcoin and the huge storm that waters the altcoins crops.