1. Experimental Design

2. Types of Variables INDEPENDENT VARIABLE (IV) ◦The thing that is intentionally CHANGED by the experimenter over the course of the investigation ◦The manipulated variable DEPENDENT VARIABLE (DV) ◦The thing that is MEASURED or OBSERVED by the experimenter ◦Is affected by the IV ◦The responding variable

3. Example Water 10” tall Orange Juice 4” tall

4. Experimental Groups  The values you choose for your independent variable  Example:  If you are studying the effect of amount of water on plant growth, the different amounts of water given to the plants are the experimental groups: 0mL, 5mL, 10 mL, 15 mL

5. Constants  Factors in an experiment that are kept the SAME and not allowed to change  Only ONE variable can be tested in a single experiment. All other variables must be held constant. Otherwise an experimenter does not know which independent variable is actually affecting the dependent variable.  Explain examples for a given experiment

6. Avoid Bias  Bias : Giving only partial information to get the results that you want  How to avoid bias? ◦ Repeated Trials ◦ Larger Sample Size ◦ Take Accurate Measurements

7. Imagine this… A weight-loss company makes a new pill that claims to help people lose 3 pounds each week. They do an experiment where they have a person, Jim, take the pills each day for a week.

8. Jim also recently joined a basketball league and has 2 games that week. Jim was also sick 2 days that week so didn’t eat for 1 whole day.

9. At the end of the week, Jim has lost 3 pounds. The company claims their pill is a success!!

10. What is wrong with this?

11. Repeated Trials  Experimental tests done more than once  Necessary to provide more accurate results; data is averaged together  Lessens the impact of human or chance error on the experimental results Example Having 5 plants for each group (experimental)

12. Hypothesis  Format:  If the IV, then the DV, because…  The “ because” part of the hypothesis is based on your prior knowledge of scientific concepts  Example : Write a hypothesis for an experiment in which you are testing to see if the drop height of a bouncy ball affects the first bounce height of the bouncy ball

13. Exit Pass Carter wants to see if the amount of food he feeds a cat affects how many naps the cat takes during a 24 hour period. Identify the IV, DV, and two constants for this experiment. Write a hypothesis for this experiment.