Experiments

An advantage of experiments over observational studies is

• An experiment can provide evidence of cause and effect.
• An experiment can compare two or more groups.
• An experiment can include explanatory and response variables.
• An experiment incorporates volunteers.

Tags

CCSS.HSS.IC.B.3

The Minnesota Study of Twins Reared Apart investigated whether attributes of twins are related to heredity or environment. The researchers assessed 56 pairs of identical twins reared apart as well as several hundred identical twins reared apart.  They compared the similarities of the twins in both groups.
Is this an experiment or an observational study?

• Experiment
• Observational study

In a famous study, 5200 patients were categorized into 2 groups according to their soda habit.  After 4-years of follow-up, the rate of heart disease was higher in the regularly drank group than the sparingly drank group.  Does soda cause heart disease?

• Yes because this is an experiment.
• No because this is an observational study.
• Can't say because this is an observational study.

Researchers believed that floral scent can sometimes improve a person's learning ability.  They set up an experiment in which each of 22 subjects completed sets of mazes.  Each subject wore a floral-scented mask and an unscented mask in random order.  The researchers measured the time to complete the sets of mazes.
What is the explanatory variable (factor)?

• The amount of scent.
• Presence or absence of the floral scent.
• Time to complete the pencil and paper mazes.
• Whether the subject was able to complete the mazes quicker while wearing the floral scented mask.

An Austrian study investigated whether maintaining a surgery patient's body temperature close to normal during surgery decreases infection rates.  Patients in the study were randomly assigned to one of two treatment groups, a normal-thermic group and a hypothermic group.
Both men and women were included in the study although it was believed that men would react differently to the treatments than women.  If the randomization to treatments was carried separately for men and women, the design would be a

• completely randomized design
• randomized block design
• matched pairs design
• systematic sample

Some people claim they can get relief from migraine headache pain by drinking a large glass of ice water. Researchers plan to enlist several people who suffer from migraines in a test. When a participant experiences a migraine headache, he or she will take a pill that may be a standard pain reliever or a placebo. Half of each group will also drink ice water. Participants will then report the level of pain relief they experience. 

• Observational Study
• Experiment

The May 4, 2000, issue of Science News reported that, contrary to popular belief, depressed individuals cry no more often in response to sad situations than nondepressed people. Researchers studied 23 men and 48 women with major depression, and 9 men and 24 women with no depression. They showed the subjects a sad film about a boy whose father has died, noting whether or not the subjects cried. Women cried more often than men, but there were no significant differences between the depressed and nondepressed groups. 

• Observational Study
• Experiment

Sources of variation in an experiment that are planned.

• extraneous variables
• factors
• treatments
• blinding

Tags

CCSS.HSS.IC.B.3

Using a placebo helps reduce

• variation
• blinding
• double-blinding
• bias

Tags

CCSS.RI.11-12.7

CCSS.RI.8.7

CCSS.RI.9-10.7

CCSS.RL.11-12.7

CCSS.RL.9-10.7

You should block by gender if you suspect the response to treatments

• is different between subjects
• is the same in both genders
• is high in each gender 
• is very different between genders