Answer: 20% according to a recent survey of 3,000 consumers by Consumer Reports.
So, what should you do if you find an error? From Motley Fool:
The process varies depending on the type and severity of the error, but the best place to start is to dispute the information with the credit bureaus. All three credit bureaus have an online dispute process, or you can write a letter if you’re more comfortable doing that.
Make sure to include any documentation that supports your claim. For identifying information, this can simply mean including a copy of your driver’s license or birth certificate. Incorrect account information can be cleared up by including a current account statement or proof that you closed the account. In cases of actual identity theft or accounts that aren’t yours, the process becomes a little trickier. If you think your identity has been stolen, the first thing to do is to put a security freeze on your credit to prevent additional fraudulent activity. Next, report the situation directly to the lender on the account. In extreme cases, you might need to contact a lawyer if you’re not getting anywhere with the creditors or credit bureaus, but most errors can be cleared up without resorting to such extreme actions.
The good news is that it is becoming easier to access your credit reports too, beyond the free access you can already get at annualcreditreport.com. From Wall Street Journal:
It’s getting easier for consumers to frequently check their credit reports for free. Credit-management website Credit Karma began allowing consumers to view their credit report from Equifax—one of the three largest credit-reporting firms in the U.S.—on Monday. This is the second credit report Credit Karma users can view as often as they like, as the website began allowing users to check their full report from TransUnion, another of the big three credit-reporting firms, in July.
Believe it or not, child identity theft is about 50X greater than it is for adults (CBS Philly), so even if you are under 18 and don’t think you have any reason to have credit report information, you should encourage your parents to check every few years to be sure you have not been victimized.