Chapter 2 Lesson 2.4 Collecting Data Sensibly 2.4: More on Experimental Design

Would the students in each section of calculus know to which treatment group, 65° or 75°, they were assigned? If the students knew about the experiment, they would probably know which treatment group they were in. So this experiment is probably NOT blinded. Room temperature experiment continued... An experiment in which the subjects do not know which treatment they were in is called a single-blind experiment. A double-blind experiment is one in which neither the subjects nor the individuals who measure the response knows which treatment is received.

In the room temperature experiment, we only have 2 treatment groups, 65° and 75°. We do NOT have a control group. Control group is an experimental group that does NOT receive any treatment. The use of a control group allows the experimenter to assess how the response variable behaves when the treatment is not used. This provides a baseline against which the treatment groups can be compared to determine whether the treatment had an effect.

Consider Anna, a waitress. She decides to perform an experiment to determine if writing “ Thank you ” on the receipt increases her tip percentage. She plans on having two groups. On one group she will write “ Thank you ” on the receipt and on the other group she will not write “ Thank you ” on the receipt. Which of these is the control group?

Suppose we want to test an herbal supplement to determine if it aided in weight loss. Why would it not be beneficial have two groups in the experiment; one that takes the supplement and a control group that takes nothing? What could be done to remedy this problem? Give one group the supplement and give the other group a pill that is the same size, color, taste, smell, etc. as the supplement, but contains no active ingredient. This is called a placebo. A placebo is something that is identical to the treatment group but contains no active ingredient.

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 Type of fertilizer Yield of crop 3

Fertilizer experiment continued: 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. Why is the same type of seed used on all 15 plots? What are other potential extraneous variables? Does this experiment have a placebo? Explain Using direct control in the experiment. Type of soil, amount of water, etc. NO – a placebo is not needed in this experiment

Fertilizer experiment revisited: A farm-product manufacturer wants to determine if the yield of a crop is different when the soil is treated with two different types of fertilizers. Twenty plots of land (10 plots are along a river and 10 plots are away from the river) 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. Can the experimenter directly control the types of soil in the different plots of land? What can be done to account for this variable? No – they must use the plots that are available They could block by type of land

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. There are 30 boxes of cake mix to use for this experiment. Experiment units? Factors? Response variable? Name the treatments? Two factors - type of pan (aluminum, glass, and plastic) and type of oven (electric and gas) How evenly the cake bakes Aluminum pan in electric oven, aluminum pan in gas oven, glass pan in electric oven, glass pan in gas oven, plastic pan in electric oven, and plastic pan in gas oven Cake mixes

Homework Pg.69: #2.52, 54, 55, 59