ap statistics 4.2d blocking and matched pairs design
TRANSCRIPT
AP STATISTICS4.2D Blocking and Matched Pairs Design
Housekeeping
Unit 1 Test Thursday and Friday (9/24 & 9/25) Multiple Choice Thursday FRQ Friday
These are timed tests—you must finish each section within the time allotted
Homework packets due ON ENTRY, Friday, 9/25
Team Time
Go over 4.2D HW
Opener: Doing Laundry
Researchers want to test whether a new detergent for clothes that require hand-washing cleans better in warm or cold water. They decide to perform an experiment using numerous pieces of dirty laundry as the experimental units. The response variable is a cleanliness rating on a scale of 0 (very dirty) to 10 (very clean).
Design a completely randomized experiment.
Opener: Doing Laundry
How should researchers deal with the fact that light-colored clothes come cleaner in cold water?
How could they ensure that after being assigned to a block, the clothes are randomly assigned a treatment?
The random assignment of experimental units to treatments is carried out separately within each block.
Many piles of dirty laundry
Assignment to blocks is NOT random
Dark-colored clothing
Light-colored clothing
Random assignment
Random assignment
Hot water
Cold water
Hot water
Compare cleanliness
Compare cleanliness
Combine results
Cold water
Why do we block?
How does blocking bring control into the laundry experiment?
Control what you can, block what you can’t control, and randomize to create comparable groups.
Matched Pairs
Common type of randomized block design. Create blocks by matching similar pairs of
experimental units (blocks of size 2). Use chance to decide which member of a pair gets
the first treatment (random assignment of treatments within each pair).
Helps reduce the effect of variation among experimental units.
Sometimes each “pair” is one experimental unit who receives two treatments. The order of the treatments is randomized for each experimental unit.
Stand Up, Sit Down! LAB
Are standing pulse rates higher than sitting pulse rates? If you received a black card, you will begin by sitting down.
If you received a red card, you will begin by standing up. When I tell you to begin, keep track of your heart rate. It
will take one minute, so please focus. Record this number. If you were standing, please sit down. If you were seated,
please stand. Again, we will record the number of heart beats in one
minute. Record your standing and sitting heart rates on your card. Turn in your card
Homework
4.2D HW: Blocking and Matched Pairs Design