Approximately what percent of American teenagers have been clinically depressed at least once by the time they enter young adulthood?

A researcher studies letters to the editor of a magazine to assess community attitudes. The research method used in this scenario can be regarded as

What will be an ideal response?

The fact that the order in which something occurs is important in establishing a cause and effect relationship is called

a. Temporal precedence b. A Sequence effect c. Co-variation of cause and effect d. An order effect