Dr. Oishi is an educational psychologist interested in students' attitudes toward math and the effect of those attitudes on performance on standardized tests. He chooses his local school district to study. There are 15 middle schools, and he randomly chooses five. Then, of the 1,500 students in each of those five schools, he randomly recruits 250 students. This is an example of which of the following sampling techniques?
A)Snowball sample
B)Systematic sample
C)Multistage sample
D)Cluster sample

How did geographical features create a civilization in china

“obamacare”: included a provision for government-run health insurance called “the public option.” was bitterly opposed by congressional republicans because most favored a “single-payer” plan. survived two challenges to its constitutionality. was partially repealed in 2013 in order to avert a government shutdown. led to the expansion of medicaid in republican controlled states.

It is widely assumed that people need to engage in intellectual activities such as solving crossword puzzles or mathematics problems in order to maintain mental sharpness as they age. in fact, however, simply talking to other people—that is, participating in social interaction, which engages many mental and perceptual skills—suffices. evidence to this effect comes from a study showing that the more social contact people report, the better their mental skills. which of the following, if true, most seriously weakens the force of the evidence cited? (a) as people grow older, they are often advised to keep exercising their physical and mental capacities in order to maintain or improve them. (b) many medical conditions and treatments that adversely affect a person's mental sharpness also tend to increase that person's social isolation. (c) many people are proficient both in social interactions and in solving mathematical problems. (d) the study did not itself collect data but analyzed data bearing on the issue from prior studies. (e) the tasks evaluating mental sharpness for which data were compiled by the study were more akin to mathematics problems than to conversation.