Your roommate is an only child. What percentage of people in industrialized countries have at least one sibling?

One of the results of the discovery that the disease syphilis and the disordered behavior that results from it are both caused by the same bacterial microorganism was

a. mental health professionals began to think that other psychological disorders might be caused by other microorganisms, and biological cures might be possible. b. individuals diagnosed with syphilis were referred to psychologists instead of doctors for further treatment. c. the mental hygiene movement was established, which attempted to provide a sterile, bacteria-free, environment for those suffering from disorders. d. mental health professionals adopted a genetic model, which has been supported by further scientific investigations into the causes of disorders.

According to the article Zipping Up the Genes about twins reared apart, when a trait is measured within a

group and some differences are found within the group, the statistic usually used to describe the differences is the (a) mean (b) average (c) variance (d) median