Although it may become the leading cause in the near future, which factor currently ranks SECOND as a cause of preventable deaths in the United States?

When designing a cross-sectional study with different age groups, a researcher is concerned

that cohort differences may influence his study results. To ease his mind, he ensures that the oldest participants ( age 80 ) are similar in intelligence, education, and social class to the younger participants. What is the researcher's primary concern? A) The older participants may not be representative of the same-aged people in the community. B) He relied on a nonprobability or convenience sample. C) It is very difficult to measure intelligence in older people. D) He should not have relied on a chain sampling method.

. With regard to temperament, "difficult children"

a. are restrained and unexpressive in their behavior. b. tend to be excessively shy. c. are moody, intense, and easily angered. d. do not fit neatly into any single category.