For more than a decade surgeons have been able to use a lase

For more than a decade, surgeons have been able to use a laser procedure to drill holes in the heart. A recent research project was conducted to see if the laser procedure can reduce chest pain. A group of 298 volunteers with severe, untreatable chest pain were randomly assigned to one of two groups: one group got the laser procedure and one group went through the setup but did not actually get the laser. The patients were sedated but awake. They could hear the doctors discuss the laser process. Each patient thought he or she was receiving the treatment. After the procedure, the patients were evaluated to determine any amount of pain relief.

1. Is this study an experiment or an observational study?

experiment

observational study

2. Does this use blocking?

yes

no

3. After the procedure, the patients were evaluated to determine any amount of pain relief. The laser patients did well. But shockingly, the other group showed more improvement than the laser group. This seems to be due to

a matched pairs design

undercoverage bias

the placebo effect

Simpson\'s paradox

Solution

1. Experiment

In an experiment investigators apply treatments to experimental units (people, animals, plots of land, etc.) and then proceed to observe the effect of the treatments on the experimental units.

2. Yes

Blocking is the arranging of experimental units in groups (blocks) that are similar to one another.

3. Placebo effect