They are correlated, but not always in the same way. On long term fro alt coins is always good Bitcoin goes up. Simply because it gives them more space to grow. For short term you can have all kinds of correlations. Right now it seems that if Bitcoin goes up or down, Alt coins goes down. When Bitcoin is steady Alt coin goes up a bit. This can change already next week. In 2017 after Bitcoin went over old ATH of $1200 Alts went up together with Bitcoin and also went up when Bitcoin was steady.