This is a follow-up to "Understanding the Financial Sector: Banks."

Many do not understand insurance companies and even more do not appreciate their benefits until forced to buy insurance or perhaps when they experience a loss and it is too late. (Consider the people who suffered great personal losses in the wake of natural disasters like Hurricane Katrina or man-made disasters like those on September 11, 2001.)

Due to the complexity and varied product lines within the insurance business, I find insurance companies to be less understood than other financial service companies. So this installment of The Finance Professor will now take a look at this industry group.

How Insurance Companies Make Money

Think of insurance companies as big casinos. The policyholder (the insured) places a bet that something will occur -- for a payment (the premium) - with the insurance company, in return for a larger payout from the insurance company that is giving greater odds that the event will not occur.

The insurance company believes that if it makes enough of these bets and receives enough premiums, then it will be able to pay off all of its insureds

and

have money left over (a profit). This is achieved though a complex set of mathematical formulas derived by specially trained mathematicians call actuaries. (When I was in high school, my father actually urged me to become an actuary.)

Back to the casino. Take a roulette table, as an example. There are 38 numbers on the "felt": 1 through 36 plus 0 and 00. If the roulette ball lands on any of those 38 numbers, you will win. However, the payoff is only 35 times your bet. But if you bet all 38 numbers, the casino would win. Why? In the long run, on average, the "house" usually wins and collects more that you would.

In simple terms, insurance companies earn money according to the following formula:

Profit (or Loss)

Equals

Plus

Investment Income

Less

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Losses Paid, Operational Costs and Taxes

Insurance companies not only make this actuarial expected return, but will also invest the premiums they receive over time to generate further profits. Historically, this money was invested in stocks, bonds and real estate. However, recently, companies such as

AIG

got caught trying to increase the yield on their returns by investing in the sub-prime mortgage markets and

mortgage-backed securities.

In doing so, they assumed far greater risk than in the past and are now feeling the pain of the credit crisis as they take huge

write-downs

on their investment portfolios.

Types of Insurers

The structures of insurance companies can come in different variations.

First we have the concept of "reinsurers." Just like a casino lays offs its risks with its peers, insurance companies can sell off some of its excess risk to specialized insurance companies call reinsurers. The worst nightmare for reinsurance companies are catastrophic events like 9/11 or Katrina.

Another variation of insurance companies comes in the form of their ownership. Most insurance companies are now owned by

shareholders and can be invested in on a public

exchange.

The minority of insurance companies are owned by the policyholders. These are called mutual insurance companies. While you can't invest in these companies on a stock exchange, you can do so by buying a policy from the insurer. For example, I own several policies in

Northwestern Mutual Life

. I earn extra

dividends in my policies and in the event that Northwest Mutual Life ever went

public I would be entitled to shares (at a favorable price) or other monetary benefits of "demutualization."

So, What's the Investment Landscape Look Like?

Not all insurance companies provide all of the products outlined above. Some offer more than one, while others specialize in a single type like health insurance. With that in mind, I will try to best identify and classify the largest and most popular insurance-focused companies below:

Life:

This type of insurance essentially provides a large payout in the event of the death of the insured.

Life insurance is probably the most stable sub-sector of the overall insurance business. The following companies have taken less risk in their investment portfolios than other insurance companies, as the life insurance business is far more stable and cost effective, and it has less exposure to the housing, mortgage and credit problems facing the broader financial services sector.

That's not to say that these companies are totally void of such risks, but they have the least exposure to them, if any. Companies to research include

ING

,

AXA

( AXA),

Prudential

,

Manulife

,

MetLife

,

China Life

,

Sun Life

and

Genworth

.

Mutual Life Companies:

Again, while you cannot invest in the stocks of these companies you

can

benefit from ownership as a policyholder, as I outlined above. In the event that these companies demutualize and go public, you may derive some monetary windfall..This windfall could be an upfront payment, shares in the company or rights to purchase shares at a discounted rate.

Some of the companies that I would look at are Northwestern Mutual,

New York Life

,

Mass Mutual

and

Penn Mutual

. Of course, having grown up watching "Wild Kingdom," I have to mention

Mutual of Omaha

.

The key to researching a mutual life insurance company is the track record of policyholder dividends and the company's

credit rating.

Property, Casualty and Liability:

These types of insurance cover the risks associated with damages to automobiles, houses, boats, buildings and other property, stemming from fire, theft, accidents or other insurable risks.

This are of insurance also covers liabilities for damages due to malfeasance of a professional, such as a doctor or attorney or the actions on the part of a corporation or its board members. Liability insurance may take other forms such as title insurance for a homeowner.

Risk management at these companies has been varied. On one hand, you have

Berkshire Hathaway

( BRK-A), which did not delve into the

mortgage-backed securities and related

derivative markets, while

American International Group

has taken huge write-downs thanks to the risks they took in the credit markets.

This is certainly a "buyer beware" part of the insurance business, but if you do your research, then you can profit wisely.

In addition to Berkshire and AIG, other stocks worth researching in this category are

Allianz

( AZ),

Travelers

,

Allstate

,

Hartford

,

Loews

( LTR),

ACE

(ACE)

,

Chubb

and

Progressive

.

As a reminder, research involves reading the company's

financial statements

and

reports

, listening to

earnings conference calls

and keeping current on

company news

.

Surety, Title and Mortgage:

With the risks associated with mortgage-backed securities and the housing bust, this is the dreg of the insurance industry right now.

If you been paying attention to the insurance business at all, the just the mention of

MBIA

,

MGIC

or

Ambac

( ABK) will probably give you shivers down your spine.

These insurers are referred to as the "monoline" insurers. Had they remained in the monoline business of insuring tax-exempt bonds, then they would have remained strong and viable companies. However, they morphed into "duoline" companies and began to insure mortgage-backed securities, in addition to their conventional business of insuring municipal securities.

As a result, these insurers are now taking huge write-downs and are

capital constrained.

Then there are the PMI (private mortgage insurance) companies which are feeling the pinch from mortgage delinquencies. These include

,

PMI Group

( PMI) and

(TGIC)

.

Some other companies in this group which may not have the same issues and you may want to investigate are

Fidelity National

,

First American

,

Old Republic

and

.

Again, because of the complex pricing of mortgage-backed securities, it's hard to know what is lurking underneath the surface of these companies' financial numbers, so be very careful.

Health Care:

These insurers provide for reimbursement of medical and dental expenses for the insured as covered by a health care plan.

The challenge with this group is the never-ending battle between rising

health care

costs and reimbursement levels.

While there are some solid companies like

UnitedHealth

, the entire group is struggling as earnings woes have swept through this business. These earnings warnings have been caused by increased costs -- much of which was attributed to a severe and late flu season

Other companies in this group include

WellPoint

(WLP)

,

Aetna

(AET)

,

Cigna

,

Humana

,

Coventry Health Care

( CVH) and

Health Net

(HNT)

.

Reinsurers:

While Berkshire is also a large reinsurer, others in this category of insurance include

Swiss Re

,

Munich Re

and

ACE

(ACE)

.

Brokers:

These companies typically just sell insurance, but may also have investment management businesses or may keep some insurance risks on their books, so

.

Some of the largest companies in this category are

Marsh & McLennan

,

Willis Group

(WSH)

,

Brown & Brown

,

Arthur J. Gallagher

and

Aon

( AOC).

As you can see, the insurance business is quite complex. With this complexity comes significant investment research. However, from that hard work you may be able to find some attractive investment opportunities amid this broad industry group.

To stay up to date on insurance companies, bookmark and don't miss TheStreet.com's Insurance section.