Understanding Blocking in AP Statistics

1. Planned, systematic variability. This is the kind we want since it includes the differences due to the treatments. 2. Chance-like variability. This is the kind our probability models allow us to live with. We can estimate the size of this variability if we plan our experiment correctly. 3. Unplanned, systematic variability. This kind threatens disaster! We deal with this variability in two ways, by randomization and by blocking. Randomization turns unplanned, systematic variation into planned, chance-like variation, while blocking turns unplanned, systematic variation into planned, systematic variation.