Speech: How Do You Know ...

. . . this?

According to the National Institute on Alcohol Abuse and Alcoholism, 4.6 million teenagers have a drinking problem.

This is kind of a trick question. You DON'T know this because the NIAAA told you, or because you read their report. You know it because Izzo cited the report, right?

So, correct attribution would be something like this:

Izzo said 4.6 million teenagers have a drinking problem, citing National Institute on Alcohol Abuse and Alcoholism figures.

Be sure to attribute a source, or even the source of a source, if need be.