One of the variables must be lurking variables.
The variables will have a correlation coefficient greater than 0.5.
There is a clear indication that a placebo effect is present in the experiment.
The investigator cannot separate the effect of the variables on a response variable.
None of these is true.
The first study was a controlled experiment, while the second was an observational study.
The first study was an observational study, while the second was a controlled experiment.
Both studies were controlled experiments.
Both studies were observational studies.
Each study was part controlled experiment and part observational study.
Yes, because each player has the same chance of being selected.
Yes, because each team is equally represented.
Yes, because this is an example of stratified sampling, which is a special case of simple random sampling.
No, because the teams are not chosen randomly.
No, because not each group of 58 players has the same chance of being selected.
I and II
I and III
II and III
I, II and III
None of the above gives the complete set of true responses.
An experiment, but with no reasonable conclusion possible about cause and effect.
An experiment, thus making cause and effect a reasonable conclusion.
An observational study, because there was no use of a control group.
An observational study, but a poorly designed one because randomization was not used.
An observational study, thus allowing a reasonable conclusion of association but not of cause and effect.
Organize the treatment and control groups.
Counteract the placebo effect.
Produce groups that are as similar as possible.
Replicate the experiment with more subjects.
Avoid the need for randomization.
The girls at your high school are surveyed to determine if they believe there is any sexual stereotyping in the school newspaper.
Two flowerpots are planted with the same type of seed. One is given 0.2 cups of water each day while the other is given 0.5 cups of water each day. At the end of one month, the growth of each plant is observed and measured.
A student flips a coin 100 times and records the number of heads.
None of these are observational studies.
The is an example of a multi-stage cluster sample.
Results from the interviews cannot be used to infer responses of the population of interest.
The population of interest is the set of all high school principals in New England.
Not every subset of principals has the same chance of selection.
All of these statements are true.
Two simple random samples are to be conducted: one of the boys in the student body and the other of the girls in the student body.
Four simple random samples are conducted: one in each of the four classes.
Two simple random samples are conducted in randomly selected homerooms: one of the boys in the selected homerooms and the other of the girls in the selected homerooms.
Two random samples are conducted: one of students whose GPA's are 2.5 or higher and the other of students whose GPA's are less than 2.5.
None of these statements is a valid design.
Simple random sample
Multi-stage cluster sample