I am a looking at a specific fund that made a killing last year. I know that this is a speculative question, but I am interested whether what I am saying held true over the years. Does a mutual fund that perform really well one year tend to do bad the following year? What evidence is there?
This can be answered by looking at the fine print for any prospectus for any stock, bond or mutual fund. It says: "Past performance is not an indicator of future performance.".
A mutual fund is a portfolio of common stocks, managed by somebody for a fee. There are many factors that can drive performance of a fund up or down. Here are a few:
I'm sure there are many more market influences that I cannot think of that push fund prices up or down. What the fund did last year is not one of them. If it were, making money in the mutual fund market would be as easy as investing in last year's winners and everyone would be doing it.
Nearly all long-lived active funds underperform the market over the long run.
The best they can hope for in almost all cases is to approximate the market return.
Considering that the market return is ~9%, this fund should be expected to do less well.
In terms of predicting future performance, if its average return is greater than the average market return, its future average return can be expected to fall.
From a mathematical point of view the stats do not change depending on past performance. Just because a fund is lucky one year doesn't mean that it will be unlucky the next.
Consider tossing a coin, the chance of heads is 50%. If you have just thrown 3 heads, the chance of heads is still 50%. It doesn't go down.
If you throw 10 heads in a row the chance of a heads is still 50%, in fact you many suspect there is something odd about the coin, if it was an unfair coin then the chance of a heads would be higher than 50%.
It could be the fund is better run, but there could be other reasons, including random chance. Some funds will randomly do better and some will randomly do worse
What you do know is that if they did better than average other funds have done worse, at least for last year.