AP Statistics - 4 Principles of Experimental Design

Comparison

comparing more than one treatment group

Why is comparison important in experimental study?

so you can tell if there is a difference in the results

Randomization

random assignment of treatment groups

Why is randomization important for experimental study?

it creates roughly equal groups and helps with unknown confounding variables (doesn’t eliminate all confounding variables)

Control

keep outside variables that might effect the results consistent

Why is control important for experimental study?

it establishes a cause and effect relationship

Replication

more data is more reliable than less data

Why is replication important?

shows patterns and trends that make results stronger

Experimental Units

who or what that are randomized and getting treatments

Changes in __________ variable cause changes in ___________ variable.

explanatory, response

Confounding variable

discuss how it effects explanatory and response variables

• ie: if one plant is in light and one is in the dark, is it the treatment or confounding variable that effects the results?

Significance of Matched Pair or Blocked vs Completely Randomized Design

Shows if the result is due to treatments or other variables that are blocked/matched pair. Easier to tease out the differences.