Across cultures, about ________% of children have ADHD, with ________ boys than girls having the disorder.

Fragile X is typical of genetic disorders in that it involves ________

a. the silencing of a gene that is critical to normal development b. building up of the X chromosome, causing it to block other chromosomes c. more severe effects in girls because they have two X chromosomes d. no noticeable effect on the patient’s life, thus making it difficult to diagnose

In an experiment, the independent variable is ____ while the dependent variable is ____

a. held constant? varied b. correlational? descriptive c. manipulated? measured d. general? specific