1. WARM - UP
An astronaut wants to examine the effects of space exposure on the percent of bone loss. The bone mass of lab rats are recorded before they are exposed to various gravity forces (.50g, .83g, 1g, and 1.5g) and various time durations (1 day, 7 days, and 28 days). There will be 4 randomly chosen rats for each combination of gravity and time period.
Is this an experiment?
What are the experimental Units?
What are the explanatory variables or factors?
What is the Response variable?
How many levels are there?
How many treatments are there?
How many experimental units are required?
Yes
The Rats
Gravity Force & Duration
% of Bone Loss
Gravity: 4 levels Duration: 3 levels 12
48 Rats

2. Chapter 13 - Experiments
Hidden Bias may occur based on how the experiment is conducted. This is reduced by using:
Single Blind Experiments – occurs when only the subjects or the people in contact with them, but not both, know which treatment a subject is receiving.
Double-Blind Experiments – neither the subjects nor the people in contact with them know which treatment a subject is receiving.
The Placebo Effect – this occurs when subjects in an experiment that are receiving a placebo, actually improve because they think they are getting the real treatment.

3. Experimental Designs
Completely Randomized Design: Every experiment should use chance to divide the experimental units into the various treatment groups.
Treatment 1
Random Assignment
Compare
Response
Variable
Experimental Units
Treatment 2
Treatment 3

4. Block Design – Experimental Units or subjects are blocked in groups of similar characteristics (Homogeneous Grouping). The random assignment of units to treatments is carried out separately within each block. Blocking reduces unwanted variation.
Block Design
Treatment 1
Compare
Response
Variable
Block 1
R.A.
Treatment 2
Treatment 3
Experimental Units
Treatment 1
Compare
Response
Variable
Block 2
R.A.
Treatment 2
Treatment 3

5. A Matched pairs design is a special case of a randomized block design
A Matched pairs design is a special case of a randomized block design. It can be used when the experiment has only two treatment conditions; and subjects can be grouped into pairs or each used twice, (getting both treatments.) Then, within each pair, subjects are randomly assigned to different treatments.
Matched Pairs Design
All Get Treatment 1
Compare the Difference in
Response Variable
Experimental Units
Randomly Assign which Treatment they get first.
All Get Treatment 2

6. HW: Page 314: (a-g)

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