Most Americans? even those who think their credit knowledge is good ? don?t understand credit scores. That?s too bad because the stakes are high, and ignorance is costly.

Everyone knows that lenders use credit scores to decide if they want to lend you money and at what interest rate. But did you know that your credit score might also determine if you get electricity for your home, can rent an apartment or even get a job?

Credit scores are used by utilities, insurers, employers, creditors and others to decide if they want you as a customer, an employee or a tenant. It is essential, therefore, that you not only know what your credit score is but what it means and how to raise it.

According to a new survey of adult Americans administered by the Opinion Research Corporation International for CFA and Providian Financial, most consumers do not understand what credit scores measure, what constitutes a good or bad score, or how scores can be improved.

Most of those surveyed understood that lenders use credit scores. But many less realize that electric utilities, home insurers and landlords often use credit scores to decide whether to sell you a service and at what price.

?Many consumers may not have taken the time to learn more about credit scores because they do not know how scores affect the availability and price of credit,? says Providian Senior Vice President Alan Elias.

For example, on a $150,000, 30-year, fixed-rate mortgage, consumers with credit scores of more than 720 might be charged a 5.72 percent rate with monthly payments of $872. But consumers with credit scores less than 560 could pay 9.29 percent with monthly payments of $1,238. That?s a difference of $4,392 per year.

Credit scores measure risk. They give a lender an idea of how much they risk to lend you money.

Two-fifths of those surveyed incorrectly believe that individuals only have one credit score. In fact, each of the three major credit bureaus ? TransUnion, Experian and Equifax ? computes separate scores. And they usually differ.

Few consumers know what constitutes a good credit score. A score less than 600 results in credit denial or a higher subprime interest rate.  Scores more than 700 usually qualify you for the lower interest rates.

Most consumers don?t understand how to improve their credit score. Many don?t realize that paying off a large credit card balance will improve a credit score. And using a credit card to the full credit line is not a good way to improve the score. If you think you can raise your credit score by marrying someone with a higher score, forget it.

As a result of the survey, CFA and Providian developed a list of critical factors they say you need to know about credit scores.

• Scores reflect only your past credit history ? not personal characteristics, such as age and gender. Over time, you have the ability to control this factor.
• A low score could not only cost you thousands of dollars a year in additional finance charges but also deny you access to credit, insurance, electric and telephone service, a rental unit or a even a job.
• Consumers with credit scores less than 600 are typically charged relatively high subprime loan rates. Those with scores more than 700 are usually pay lower rates. Those with scores more than 760 get the lowest rates of all.
• Paying your bills consistently and on time is the best way to improve your credit score. If you are behind, get current and stay there. Don?t max-out credit cards and other revolving credit. Pay off debt rather than moving it around, and don?t open many new accounts.
• Check your credit report annually to see that it?s error free. Remember that while you often can get a free credit report, you almost always must pay for a credit score (except when applying for a mortgage loan). It usually costs around $9 to purchase reports and scores from one of the big three credit bureaus.