1. 4.2 Today you will work with your group to design an experiment. But first….There are a few things you need to know. 1)Observational study – The researcher observes outcomes without imposing any treatment. 2)Experiment – The researcher actively imposes some treatment in order to observe the response. 3) In every experiment, you must clearly identify your explanatory and response variables.

2. Designing your experiment 1)You have 5 min. to design an experiment appropriate for the given scenario. *Be as descriptive as possible so that another person could implement your experiment exactly as you plan to. 2) You will join with another group that has your same scenario (same color paper). Each group will have 2 -3 min. to describe their experiment to the other group. The listening group members should take notes as they listen. 3) Once both groups have presented, each group may offer advice on ways to improve the other group’s experiment. *You will need to select a presenter for your group

3. Designing your experiment 4) You will then learn about the details of experimental design with the 4.2 notes. 5) During the lesson, keep your experiment in mind as you will be given a chance to make improvements to your design prior to turning it in. *This lesson will take two days. Your experiments are not due until tomorrow, but you will turn them in today at the end of the hour so I can check your progress.

4. 4.2 Designing Experiments After this lesson you should be able to: Name and describe components of experiments Diagram an experiment

5. I’ve developed a new rabbit food, Hippity Hop. Rabbit Food Makes fur soft & shiny! Increases growth! Better than any other rabbit food out there

6. Hippity Hop I’ll use my pet rabbit, Lucky! Since Lucky’s coat is softer & he has more energy, then Hippity Hop is a better rabbit food! Can I just make these claims?

7. What must I do to make these claims? Who (what) should I test this on? What do I measure (response variable)? Do an experiment Rabbits Chose one variable that will be “evidence” that your food is better or not. Weight Gain, How soft fur is? Energy level, etc I’ll choose Weight Gain

8. Experimental unit – the individual (person, animal, object, etc.) to which the treatments are assigned. Experimental units who are human beings are called Subjects. More definitions:

9. Response variable – what you are measuring Treatment – a specific experimental condition applied to the units Factor – the specific levels of the explanatory variables

10. I plan to test my new rabbit food by doing an experiment. What are my experimental units? What is the response variable? Rabbits How well they grow….(weight gain)

11. Control group – a group that is used to compare the explanatory variable against; can be a placebo or the “old” or current item on the market Definitions continued:

12. Old Food Hippity Hop Now I’ll use Lucky & my friend’s rabbit, Flash. Lucky gets Hippity Hop food & Flash gets the old rabbit food. WOW! Lucky is bigger so Hippity Hop is better! Lucky Flash

13. Measurements are usually subject to variation. Use enough subjects or units to reduce variation. Replication – the practice of assigning each treatment to many experimental units.

14. Old Food Hippity Hop The first five rabbits that I catch will get Hippity Hop food and the remaining five will get the old food. The Hippity Hop rabbits have higher weights so it’s the better food!

15. Randomization – The use of chance to assign experimental units to treatment groups. Systematic differences among the groups of experimental units in a comparative experiment cause bias. Randomize to reduce bias.

16. Old Food Hippity Hop 3 5 78 9 4126 10 I evaluated the rabbits & found that the rabbits eating Hippity Hop are gaining more weight than the rabbits eating the old food! 97 9 7 5 83 6 1 2 10 4 583 Number the rabbits from 1 – 10. Place the numbers in a hat. The first five numbers pulled from the hat will be the rabbits that get Hippity Hop food. The remaining rabbits get the old food.

17. Principles of Experimental Design Control Replication Randomization The ONLY way to show cause & effect is with a well-designed, well-controlled experiment! - reduces bias by spreading any uncontrolled confounding variables evenly throughout the treatment groups.

18. Placebo – a “dummy” treatment that can have no physical effect. Placebo Effect – a measurable, improvement not attributable to a treatment that has been administered. Definitions…almost done

19. blinding - method used so that units do not know which treatment they are getting double blind - neither the units nor the evaluator know which treatment a subject received

20. Suppose we wish to test a new deodorant against one currently on the market.

21. 10 people Random Assignment Treatment A New Deodorant Treatment B Old Deodorant Group 1 Group 2 Compare Perspiration amount Completely Randomized Experiment

22. Treatment B Randomly assign experimental units to treatments Treatment A Completely randomized design

23. 20 total people Treatment A New Deodorant Treatment B Old Deodorant Treatment A New Deodorant Treatment B Old Deodorant Random Assignment Block A 10 Female Block B 10 Male Compare Perspiration amount Block Design– units are blocked into groups and then randomly assigned to treatments. Compare Perspiration amount Blocking also helps reduce variability.

24. –match up experimental units according to similar characteristics & randomly assign one to one treatment & the other automatically gets the 2nd treatment –OR have each unit do both treatments in random order Matched pairs - a special type ofMatched pairs - a special type of block design block design

25. Pair experimental units according to specific characteristics. Next, randomly assign one unit from a pair to Treatment A. The other unit gets Treatment B. Treatment A Treatment B This is one way to do a matched pairs design – another way is to have the individual unit do both treatments (as in a taste test).

26. Example 1: A farm-product manufacturer wants to determine if the yield of a crop is different when the soil is treated with three different types of fertilizers. Fifteen similar plots of land are planted with the same type of seed but are fertilized differently. At the end of the growing season, the mean yield from the sample plots is compared. Experimental units? Factors? Response variable? How many treatments? Plots of land Fertilizer types A, B, & C Yield of crop 3 Diagram the experiment using a Completely Randomized Design

27. 15 Plots Group 1 5 plots Group 2 5 plots Group 3 5 plots Fertilizer A Fertilizer B Fertilizer C Compare Yield of crop Random Allocation Why is the same type of seed used on all 15 plots? What are other potential extraneous (lurking) variables? It is part of the “control” in the experiment. Type of soil, amount of water, etc.

28. Example 2: A consumer group wants to test cake pans to see which works the best (bakes evenly). It will test aluminum, glass, and plastic pans in both gas and electric ovens. Experiment units? Factors? Response variable? Number of treatments? Two factors - type of pan & type of oven Type of pan has 3 levels (aluminum, glass, & plastic) & Type of oven has 2 levels (electric & gas) How evenly the cake bakes 6 Cake batter

29. Example 3: Four new word-processing programs are to be compared by measuring the speed with which standard tasks can be completed. One hundred volunteers are randomly assigned to one of the four programs and their speeds are measured. Is this an experiment? Why or why not? What type of design is this? Factors? Response variable? Yes, a treatment is imposed. Completely randomized one factor: word-processing program with 4 levels speed

30. Example 4: Four new word-processing programs are to be compared by measuring the speed with which standard tasks can be completed. One hundred volunteers are randomly assigned to one of the four programs and their speeds are measured. Is there a potential confounding variable? Can this design be improved? Explain. YES, the speed at which they could type already You could do a block design where each person uses each program in random order.

31. Example 5: Suppose that the manufacturer wants to test a new fertilizer against the current one on the market. Ten 2-acre plots of land scattered throughout the county are used. Each plot is subdivided into two subplots, one of which is treated with the current fertilizer, and the other with the new fertilizer. Wheat is planted and the crop yields are measured. What type of design is this? When does randomization occur? Matched - pairs design Randomly assigned treatment to first acre of each two-acre plot

32. Larger samples produce statistics with less variability. Blocking also helps reduce variability. Name two ways to reduce variability?

33. 4.2 Designing Experiments I can identify components of experiments I can diagram an experiment Homework: # 45–56, 61–63, 67, 72, 77, 78, 84