A two-tailed test is chosen over a one-tailed test a. in most ...

[kwoodring]

A two-tailed test is chosen over a one-tailed test
 
  a. in most studies.
  b. when a researcher does not have a good idea of where the sample mean will fall.
  c. when the researcher knows a sample mean will fall in one of the tails.
  d. when a researcher has a clear idea of the tail in which the sample mean will fall.

Question 2

When neither the subjects nor the experimenter are aware of which group is
  experimental and which is control, then the study is said to be
 
  a. contaminated
  b. confounded
  c. concealed
  d. double-blind

[welcom1000]

Answer to Question 1

b

Answer to Question 2

d