How mutual fund ads try to fool you?

You would have noticed all those mutual fund ads that quote their amazingly high one-year rates of return. Your first thought is "wow, that mutual fund did great!" Well, yes it did great last year, but then you look at the three-year performance, which is lower, and the five year, which is yet even lower. What's the underlying story here? Let's look at a real example. These figures came from a local paper:

1 year - 53%
3 year - 20%
5 year - 11%

Last year, the fund had excellent performance at 53%. But in the past three years the average annual return was 20%. What did it do in years 1 and 2 to bring the average return down to 20%? Some simple math shows us that the fund made an average return of 3.5% over those first two years: 20% = (53% + 3.5% + 3.5%)/3. Because that is only an average, it is very possible that the fund lost money in one of those years.

It gets worse when we look at the five-year performance. We know that in the last year the fund returned 53% and in years 2 and 3 we are guessing it returned around 3.5%. So what happened in years 4 and 5 to bring the average return down to 11%? Again, by doing some simple calculations we find that the fund must have lost money, an average of -2.5% each year of those two years: 11% = (53% + 3.5% + 3.5% - 2.5% - 2.5%)/5. Now the fund's performance doesn't look so good!

It should be mentioned that, for the sake of simplicity, this example, besides making some big assumptions, doesn't include calculating compound interest. Still, the point wasn't to be technically accurate but to demonstrate how misleading mutual fund ads can be. A fund that loses money for a few years can bump the average up significantly with one or two strong years.