Designing Good ExperimentsDo Now: Please copy the following definitions into your

notes:

Dependent Variable: The variable in an experiment which is measured as a result. It’s value depends on the

value of the independent variable (example: how long termites followed an ink trail)

Independent Variable: The variable in an experiment whose values are selected by the experimenter. Finding the effect that changing this variable has is the purpose

of an experiment (example: ink color)

Control Group: The samples or trials in an experiment that DO NOT get any experimental treatment. It is what the other groups will be compared to. (example: termite

behavior with no trail)

Know your Variables!• Jeff wants to figure out the effect of using hand

sanitizer on the number of bacteria on his hands. • He will measure the number of bacteria by putting his

hand on a petri dish and then counting how many bacteria have grown there 3 days later.

• He does three trials of the experiment: one without using any sanitizer, one with “brand x” sanitizer, and one with “brand y.”

• What are the independent and dependent variables of the experiment?

• What is the control group?

Milgrim’s Weird (& Disturbing) Experiment

• As we watch the video about the famous Milgrim psychology experiment, ask yourself:– What is the independent variable?– What is the dependent variable?– What is the control group? / Is there a control

group?

Refresher

• Independent Variable: selected by experimenter trying to figure out what effect it has.

• Dependent Variable: measures the effect of the independent variable.

• Control Group: gets no experimental treatment. Independent variable = “0”