NOTE SHEET 1 – Designing Controlled Experiments

Why?

Scientists can solve problems and test theories by designing and performing controlled experiments In a controlled experiment, the scientist chooses something to test (an independent variable) to see if it causes a change in something else that they will measure (the dependent variable) The experiment is controlled because the scientist makes sure that all experimental variables are kept constant and only changes the independent variable By doing this, the scientist makes sure that the dependent variable can only change if the independent variable causes it to do so

Designing Controlled Experiments For example, a scientist could see if caffeine (IV) affects growth (DV) in mice

A controlled experiment has 4 basic parts: THE PROBLEM – What are you trying to find out? Independent Variable (IV) – What is tested to see if it has an effect on something else Dependent Variable (DV) – What is affected or changed because of the IV – The DV in a controlled experiment is what you measure as your data Problem Statement – Question that relates the IV to the DV How will the IV affect the DV ?

Hypothesis A hypothesis is a prediction based on prior research about what will happen during the experiment For the problem “How will caffeine affect growth in mice?” there are a few possible hypotheses: The caffeine will have a negative effect on the growth of the mice The caffeine will have a positive effect on the growth of the mice The caffeine will have no effect on the growth of the mice

A controlled experiment has 4 basic parts: THE EXPERIMENTAL DESIGN (or PROCEDURE) – What are you going to do to investigate the problem? The procedure is the steps you are going to follow to do the experiment A good procedure is: clearly written in numbered steps as precise and exact as possible (include measurements, units, etc.) easily repeated by somebody else

Why does the procedure have to be as precise and exact as possible? Consider the following cake recipe: Ingredients: sugar, butter, eggs, vanilla extract, flour, baking powder, milk Directions: Heat oven and grease pan. Mix sugar and butter, add eggs and stir in vanilla. Combine flour and baking powder and add to sugar mixture. Add milk and stir. Pour batter into pan and bake. What is wrong with this recipe?

A Better Recipe Directions Ingredients 1 cup white sugar ½ cup butter Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x9 inch pan or line a muffin pan with paper liners. In a medium bowl, cream together the sugar and butter. Beat in the eggs, one at a time, then stir in the vanilla. Combine flour and baking powder, add to the creamed mixture and mix well. Finally stir in the milk until batter is smooth. Pour or spoon batter into prepared pan. Bake for 30 to 40 minutes in the preheated oven. For cupcakes, bake 20 to 25 minutes. Cake is done when it springs back to the touch. Ingredients 1 cup white sugar ½ cup butter 2 eggs 2 teaspoons vanilla extract 1 ½ cups all purpose flour 1 ¾ teaspoons baking powder ½ cup milk

Mmmm…Cake

Experimental Design Continued Constant – Variables in the experiment that remain the same each trial Control – A test group without the IV used for comparison to see if the IV really has any affect on the DV Repeated Trials – Doing tests more than once to get more accurate data

If you ALWAYS wash your hair with shampoo, how do you know if it actually works? If you try washing your hair with just water, and it looks and feels the same, does the shampoo do anything? Would you know this without trying just water? In this example, using water only would be considered a control – this way you would know if the shampoo works better or worse than nothing at all Does shampoo work?

If you flip a coin one time and get heads, is this a correct conclusion: Every time you flip a coin, you get heads If you flip the coin a few more times, eventually you will get a tails If you get a result once, it is meaningless, but if the experiment is repeated and the results are always the same, then that result is reliable Why repeat trials?

A controlled experiment has 4 basic parts: THE DATA – A measure of the IV’s effect on the DV Data is collected and presented in a Data Table AND a Graph

Data Table and Graph In a data table, the IV goes in the left column and the DV goes in the right column In a graph, the IV is on the X-axis (bottom) and the DV is on the Y-axis (left side)

A controlled experiment has 4 basic parts: THE CONCLUSION – An answer to the problem A conclusion uses data to answer the question asked by the problem statement and discusses the experiment’s validity A good conclusion is always supported by data from the graph and data table

Why do I need to back up the conclusion with data? Consider the following statement by itself: Michael Jordan is the greatest basketball player in the history of the NBA

The Same Statement With Data Michael Jordan is the greatest basketball player in the history of the NBA NBA 50th Anniversary All-Time Team (1996) Member of six NBA championship teams (1991-93, 1996-98) Five-time NBA Most Valuable Player (1988, 1991-92, 1996, 1998) Six-time NBA Finals Most Valuable Player (1991-93, 1996-98) Ten-time All-NBA First Team (1987-93, 1996-98) All-NBA Second team (1985)

Michael Jordan is the greatest… Three-time NBA All-Star Game MVP (1988, 1996, 1998) Participated in 11 NBA All-Star Games (1985, 1987-1993, 1996-98), starting 10 times, and missed another due to injury Holds the NBA All-Star Game career record for highest scoring average (21.3 ppg) Recorded only triple-double in All-Star Game history, with 14 points, 11 rebounds and 11 assists, in the 1997 NBA All-Star Game in Cleveland Michael Jordan is the greatest… Nine-time NBA All-Defensive First Team (1987-93, 1996-98) NBA Defensive Player of the Year (1988) NBA Rookie of the Year (1985) NBA All-Rookie Team (1985) Two-time IBM Award winner, for all-around contribution to team's success (1985, 1989)

Michael Jordan is the greatest… Scored his 29,000th career point, posting a game-high 41 points, 6 rebounds and 4 assists, in a 107-93 win over the Minnesota Timberwolves on 4/3 Broke Kareem Abdul-Jabbar's NBA record by scoring in double-digits for the 788th consecutive game, scoring a game-high 33 points, against the Minnesota Timberwolves on 12/30/97 Scored a career-high 69 points in a 117-113 overtime win at Cleveland on 3/28/90 Michael Jordan is the greatest… Won the Nestle Crunch Slam Dunk in 1987 and 1988, also participating in 1985 Passed Kareem Abdul-Jabbar to become the NBA's all-time leading playoff scorer (5,762 points) during the 1998 Eastern Conference Finals Passed Dennis Johnson into fourth place on the NBA's all-time playoff assists list (1,006), in an 88-83 victory over the Indiana Pacers in Game 7 of the Eastern Conference Finals in 1997-98

The Conclusion Continued - Validity Validity – How reliable are the results of an experiment? Results are more reliable, or valid, when: the experiment is repeated more than once (repeated trials) The experiment is carefully designed and performed The experiment keeps all variables constant (except for the IV)

The results of an experiment are not valid if… All the variables in the experiment are not carefully controlled The procedure does not include measurements The experiment is done only one time If mistakes are made during the experiment that might affect the results

Experimental Scenario A science teacher heard a rumor that students listening to classical music perform better on tests. He decides to test this theory when he gives his next test to his class, which contains 20 students. Design a controlled experiment to test this theory. Directions First, state the problem and identify the variables. Second, write a numbered procedure that shows how the experiment will be performed.

Experimental Scenario Problem Statement How will listening to classical music affect the student’s performance on tests? IV is listening to classical music DV is student’s performance on tests