2E

Skill or Concept: I can . . . Questions to check your understanding Rating
from 1 to 5
Identify the key components of an experiment. 1
Determine whether or not an experiment has been designed well. 2
Use a diagram to illustrate the design of a given experiment. 3
Determine factors, other than the factor of interest, that could have an effect on the response variable of a given experiment (nuisance factors). 4
Identify blocks in a specified experiment. 5

A flowchart. The first box reads "Experimental units: 401,974 subjects." It has two arrows coming out of it, both arrows are labeled "randomly assigned." One of the arrows goes to a box with text reading "Experimental Group" and the other to another box reading "Control Group." Both of these have arrows leading to another box that has nothing written in it. A flowchart that begins with "Experimental Units." From here, there are three arrows, to a column of boxes labeled "Block 1," "Block 2," and "Block 3." Block 1 has three arrows leading to different boxes, labeled "Group 1," Group 2," and "Group 3," respectively. These all have arrows leading to the same box, which has nothing written in it. "Block 2" and "Block 3" have the same pattern of arrows and boxes as "Block 1." The top 2 unlabeled boxes are also connected with an arrow pointing both directions. A flowchart. On the far left is "Experimental Units," which has two arrows leading from it to boxes labeled "Block 1" and "Block 2," respectively. "Block 1" has an arrow leading to a box labeled "Experimental Group" and another to a box labeled "Control Group." "Experimental Group" and "Control Group" each have an arrow leading from them to the same blank box. From "Block 2," there is an arrow leading to a different box labeled "Experimental Group" and another box labeled "Treatment 2" Both of these boxes have an arrow leading to a different blank box. The two blank boxes have a two-way arrow between them.

Glossary

completely randomized block design
a design where the experimental units are divided into homogeneous groups called blocks and within each block, the experimental units are randomly assigned to treatments.
placebo
a harmless version of the treatment that does not contain any active ingredients(e.g., a sugar pill).
placebo effect
a positive response that people who believe they are receiving treatment for a condition have, even if what they are actually receiving is a placebo.
blinding
nondisclosure of the treatment an experimental unit is receiving.
double-blind
when neither the subject nor those having contact with the subject know the treatment assignment.
block
a group of subjects that are similar, but blocks differ in ways that might affect the outcome of the experiment.
blocking
grouping together of homogeneous (similar) experimental units followed by the random assignment of the experimental units within each group to a treatment.