The control group

• What is the control group?

• Ex: you are testing whether putting a plant under a bright lamp makes it grow faster.– Independent variable:– Control group:– Dependent variable:

The control group is missing the variable you are testing!

• You wonder whether putting salt on a cucumber will keep it from rotting?– Independent variable:– Control group:– Dependent variable:

The control group

• Does eating five KitKats after dinner make your sister fall asleep earlier than usual?– Independent variable:– Control group:– Dependent variable:

The control group

So what does a control group tell you?

• Tells you whether your independent variable actually had an effect!– It somehow affected the group you were testing– Example: Your sister and the KitKats

Group VariableResult (time she fell

asleep)

Control None (no KitKats) 8 p.m.

Experimental 5 KitKats 10:30 p.m.

Experiment 1

• Did eating KitKats have an effect on what time your sister fell asleep?

• How do you know?

Group VariableResult

(time she fell asleep)

Result (time she

fell asleep)

Result (time she

fell asleep)

ControlNone (no KitKats)

8 p.m. 8 p.m. 8 p.m.

Experimental 5 KitKats 10:30 p.m. 8 p.m. 8 p.m.

Experiment 1 Experiment 2 Experiment 3

Control group

• If the results of a control group and experimental group are the same, the variable has no effect.

• If the results of a control group and experimental group are DIFFERENT, the variable has an effect.