Index funds are a hot topic for mutual fund investors because there is a growing belief that index funds will outperform actively managed funds within their respective categories (e.g. a fund that invests in small cap funds would underperform a small cap index fund). A lot of academic research has been done on this topic — more than the scope of this post (and site, in fact) can bear. Between the Efficiency Hypothesis and the Purity Hypothesis, most people can find the answers to their questions.

Why Index Funds Matter

Index funds are an interesting breed and a lot of people swear by their cost to performance ratio. Since index funds simply mirror an index (there is no real research involved, no “intelligence” since it has already been done by the appropriate index, like the S&P 500, the Russell 2000, etc.) these funds are the cheapest in terms expenses.

Cost is a huge factor when it comes to index funds.

What many investors argue is that actively managed mutual funds try to beat the index. Sometimes they win, sometimes they lose and statistically speaking it becomes less and less likely every year that they beat the index to repeat their performance. So, since sometimes they win and sometimes they lose, why not simply own the index and enjoy steadier returns?

So Why Bother With Actively Managed Funds?

Indeed, knowing the above information may make an actively managed fund seem like a big and expensive risk. However, there is a lot to be said about active management, particularly for people who believe in the fund manager who operates and oversees the fund (see our archived post about Anthony Bolton, arguably one of the sharpest investment managers around). When investors have such faith in a manager, they realize that they can employ that person for a fairly low price… even if it is a two, three or even four times the cost of a bland, regular index fund.

The prolific managers are not the sole reason why some people will choose an actively managed fund over an index fund. Since many funds can shift their positions fairly easily, they can often take advantage of market inefficiencies, whereas index funds are stuck owning whatever it is that they own. There is no flexibility to safeguard investors against security specific risks.

Not that these are exhaustive reasons, but they provide the starting point as to why so many investors might chose one type of mutual fund over another.

What The Purity Hypothesis Tells Us

That brings us to Beta. Now, according to William Thatcher, a Senior Consultant at Hammond Associates in St. Louis, MO, Beta can tell us whether or not our actively managed funds will outperform an index fund. But there is one catch: that the performance strength index in particular is a known factor.

How this works is as follows: Suppose small cap stocks are a strong performer in a given year. Based on the Beta of your small cap fund, you will know whether your fund outperformed or underperformed the index funds for small cap stocks. If your fund’s Beta is less than 1 (considered less style pure than the index) then it will underperform the index (and vice versa if Beta is greater than 1).

This makes sense of course. But what it also tells us is that an investor would need to accept a fair amount more risk in order to invest in a fund that has a Beta greater than 1.

The Purity Hypothesis takes things one step farther in demonstrating how to invest, whether in Index funds or actively managed funds. The problem again is trying to determine ahead of time what asset classes will perform strongest for any given year. Because if that much can be determined, then an investor can minimize risk while simultaneously improve returns by:

1. Investing in Index fund for the best-performing asset class (e.g. large, mid and small cap stocks or funds)
2. Investing in Index funds for the three investment styles for that group (e.g. value, blend and growth)
3. Investing in actively managed funds for the poorest-performing asset group (e.g. large, mid and small cap stocks or funds)
4. Investing in actively managed funds for the three investment styles for that group (e.g. value, blend and growth)

The theory presented here finds it support in Thatcher’s research and for the most part can be substantiated by back-testing (I say for the most part because I did not go back to every single period in history to back-test). And of course it makes a great deal of sense because on a risk-adjusted basis, the Index will always outperform active funds when that asset class it outperforming other asset classes. (Click to read the Full Report).

So, whether your mutual funds invests in small cap stocks or follow a particular index, if you can determine which asset class will outperform the market and which classes will fall behind, you can actually achieve great returns (and save a few bucks) by choosing index funds for the top-performing classes and actively managed funds for the poorest-performing classes.