NEW YORK (CNN/Money) - I have read that narrowly focused insurance policies, such as cancer insurance, are not a good buy. How can I convince my daughter of that?

-- Sally Beckman, Richmond, Virginia

As a matter of logic and economics, it's hard to make a good case for cancer insurance. It makes no more sense than, say, buying collision insurance only on the left front bumper of your car as opposed to a policy that covers damage on the car overall.

On the other hand, when it comes to the big C, people often don't think logically, which is understandable considering the awful effects this disease can have, physically and financially. Frankly, I think the insurers that peddle this kind of insurance try to capitalize on people's fears about the disease by rattling off a lot of scary facts and hoping to generate an emotional rather than a rational response.

If I were in your position, I guess I would begin my case against cancer insurance by explaining that it's just not an efficient way to buy insurance. I mean, if it truly makes sense to buy a separate cancer policy, then why not a heart disease policy and a kidney failure policy and a diabetes policy too?

Clearly, trying to insure specific diseases is little more than a guessing game about what kind of medical treatment we're likely to need in the future and how we're likely to die. This approach would also get expensive as you pay individual premiums on each narrow sliver of coverage.

I'd go on to explain that that while cancer is a real threat to most Americans, it's not a given you'll contract it. Yes, three in ten Americans get cancer over their lifetime but seven in ten will not. Obviously, your odds of getting this disease will vary depending on your family history and the way you live your life. But overall, according to the National Association of Insurance Commissioners, the odds are against you receiving benefits from a cancer policy.

Next, I'd point out that there's often less than meets the eye with these policies -- that is, there are lots of limitations to the benefits touted in the brochure. Some pay only for care while hospitalized, a dubious benefit since these days many treatments are delivered on an outpatient basis. Others promise to increase coverage after you've been hospitalized 90 days.

But the average hospital stay for cancer patients is less than two weeks. So even if you're convinced you're going to contract cancer and ought to have such a policy, you may not end up collecting on some of the benefits in the policy.

Finally, I'd explain that you're much better off with much broader coverage that covers you against a variety of risks. So for starters, you would want a health insurance plan through your employer or that you buy on your own that, typically after a deductible or co-payment of some sort, covers visits to the doctor and treatment at a hospital for virtually all illnesses and diseases.

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As part of that plan or as separate coverage, you would also want a major medical policy that covers you in the event of catastrophic medical costs you might incur because of an accident or a disease or condition requiring expensive procedures and perhaps long-term care. These types of coverage would likely cost more than a cancer policy, but they cover much more and are considered a better buy. Assuming you have children or others depending on your income, you would also want a life insurance policy that would pay off in the event of your death, regardless of the cause.

If your daughter is like most Americans, she'll find it tough enough to pay premiums for the health and life insurance coverage she really needs. Why make matters more difficult by diverting money for a policy she can do without?

Walter Updegrave is the author of Investing for the Financially Challenged and can be seen regularly Monday mornings at 8:40 am on CNNfn.