1. Catalyst (4 min) 1. Why is it important to communicate your results after you perform a lab experiment? 2. What do we do if our results do not support our hypothesis?

2. Where are we? Last week: Observation  How we collect data in the lab Yesterday: Scientific Method  How we solve problems in the lab Today: Experiment Design  How we design a procedure to solve problems

3. Experiment Design 9/21/10

4. Elements of a good experiment Control Independent Variable Dependent Variable Beriberi Scientists thought bacteria caused Beriberi Injected a group of chickens with bacteria Left one group of chickens alone Observed which chickens got sick

5. Independent Variable A change caused by the scientist Beriberi Scientists thought bacteria caused Beriberi Injected a group of chickens with bacteria Left one group of chickens alone Observed which chickens got sick

6. Dependent Variable A variable whose value depends upon the independent variable What we observe in the lab Beriberi Scientists thought bacteria caused Beriberi Injected a group of chickens with bacteria Left one group of chickens alone Observed which chickens got sick

7. Control The standard that is used for comparison Beriberi Scientists thought bacteria caused Beriberi Injected a group of chickens with bacteria Left one group of chickens alone Observed which chickens got sick

8. Constant Something that is held the same throughout the experiment In order to make sure we know exactly what’s causing a change, we can only alter one variable at a time! Examples The number of chickens The amount of bacteria injected What all of the chickens ate