Experimental Design The Scientific Method

TitleTitle Describes what the experiment is aboutDescribes what the experiment is about The Effect of the IV on the DVThe Effect of the IV on the DV

HypothesisHypothesis Educated guess about what will happen in a certain situationEducated guess about what will happen in a certain situation If the IV, then the DVIf the IV, then the DV

Theory VS. Hypothesis A theory is an explanation of observable events or facts for which no exception has been found A hypothesis is a statement that can be tested. (an educated prediction)

Independent Variable The part that is purposely changed (I change the IV)The part that is purposely changed (I change the IV) What will you add or change?What will you add or change? “The IV is controlled by me”“The IV is controlled by me”

Dependent Variable The variable that responds to changeThe variable that responds to change What happened? What did you measure?What happened? What did you measure? “The DV is the results I see”“The DV is the results I see”

Levels of IV The levels of the thing you are changingThe levels of the thing you are changing Amount of water (20 mL, 40 Ml, 60 mL), amount of light (10 mins, 20 mins, 30 mins)Amount of water (20 mL, 40 Ml, 60 mL), amount of light (10 mins, 20 mins, 30 mins)

Practice: What is the IV? What is the DV? What are the levels of the IV?

TrialsTrials Number of times the experiment is doneNumber of times the experiment is done Are the results accurate?Are the results accurate? Did you try the experiment enough times?Did you try the experiment enough times?

Control Group Used for comparison (under NORMAL conditions)Used for comparison (under NORMAL conditions) IV is NOT appliedIV is NOT applied “regular” group. Usually tested 1 st (not always though!)“regular” group. Usually tested 1 st (not always though!)

ConstantConstant Factors that do NOT change in any part of the experimentFactors that do NOT change in any part of the experiment What was kept the same at each trial?What was kept the same at each trial?

Scenario 1/3 People who smoke cigarettes have a higher incidence of lung cancer. At risk children who attend Head Start get better grades in reading in the 2 nd grade. People who have used cell phones for at least 10 years have an increased risk of developing a brain tumor Walking steps a day will lower your blood pressure

Scenario 2/3 Suzie Q wants to know the effect of different colors of light on the growth of plants. She believes that plants can survive best in white light. She buys 5 ferns of the same species, which are all approximately the same age and height. She places one in white light, one in blue light, one in green light, one in red light and one in the closet. All of the ferns are planted in Miracle-Grow and given 20 mL of water once a day for 2 weeks. After the two weeks, Suzie observes the plants and makes measurements.

Scenario 3/3 William notices that Scooby solves most of his mysteries while eating Scooby snacks. He wants to know if Scooby can solve mysteries while eating any other type of snack. He designs an experiment to test the effect of the type of treat on Scooby’s ability to solve a case. He decides to give Scooby four cases involving disappearing socks. For each case he changes the type of snack: Original Scooby snacks, chicken nuggets, beef jerky, and rawhide sticks. He gives Scooby 1 month to solve each case and allows Scooby to work with his gang each time. William records if the case was solved while using each of the different types of snacks.