We are often told that "speed never slumps", and the cliche itself is almost certainly true. While batting statistics go up and down in both small and large sample sizes, you wouldn't expect actual speed to have highs and lows (unless the player is injured). The implication of "speed never slumps" is usually that faster players go through less offensive slumps than those that are not fast. In fact, in a conversation about Yasiel Puig, I heard one commentator say that he shouldn't have long slumps because he runs well. The thought process is usually that when the fast player is "cold" at the plate, they will still beat out infield hits and be able to get on base with bunts. So I wanted to look at whether or not speed hitters go into slumps more than power hitters. I couldn't find any articles that actually tested this, there was one on defense, but couldn't find one on speed. There may be some out there, but hopefully they tested it differently (that is, I don't think I am copying anyone's ideas and did all my own work, but I am sure I am missing plenty of studies that I couldn't find. If you know of any good ones, leave them in the comments).
So I used FanGraphs leaderboards, and looked at the 694 qualified hitters since 2000, took the top 30 players by ISO and compared it to the top 30 hitters by speed score. I then looked at month by month (because this is easy to do with the FanGraphs leaderboards, and I had no idea what amount of time I should look at for slumps and cold streaks) for the 60 players, and used the standard deviation of all the months by wRC +, in order to measure the player offensively as a whole. I did this year by year, because skill sets obviously change over years. Then I used the average standard deviation of each year, followed by the average standard deviation of each group of 30 years. If you want to check my work, here are both sheets:
If the thesis that speed players slump offensively less was true, we would expect a smaller standard deviation from that group. That isn't what we got using this method though, with the power guys slumping slightly less. Dewayne Wise and Mike Trout (small sample size) seem to be the most streaky guys from month to month in the speed group, with Russell Branyan being the streakiest power guy. The most consistent power hitter was Alex Rodriguez, with Juan Pierre and Ben Revere (just 2 years of sample size) being the most consistent speed players.