Additional Principles of Experimental Design Answers

A study is testing the effectiveness of a new allergy medication. Sixty volunteers who reported they experience allergies were randomly assigned to one of two groups: one with the new medication, and another with a placebo. After two weeks, the subjects’ level of allergic symptoms was surveyed.

A farmer learns of a new type of corn that is supposed to have a higher yield of ears. From previous crops, he knows approximately how many ears of corn 10 plants will produce from the original seeds. The farmer decides to plant the new type of corn to determine if the seeds will produce a higher number of ears of corn. He plants the first 100 seeds of the new type of corn seeds in the field he uses for corn. When it is time to harvest, he randomly selects 10 plants and counts the number of ears. The farmer compares the number of ears with the yield he received the previous year from 10 plants using the original corn seeds. Because the new type of corn produced a higher number of ears, he concludes that the new type of corn does produce more ears of corn. Which of the following statements is not true about this experimental design?

A student wants to determine if different types of soil, A and B, affect the propagation of African violets. One hundred leaves from the same variety of African violet were selected. The leaves were then randomly assigned to 50 pots with type A soil and the remaining leaves were put into the 50 pots with type B soil. All of the pots were given the same amount of water and arranged in 10 rows of 10 pots near a window for light. The 50 pots with type A soil were placed closest to the window. At the end of two months, the pots with type A soil had the greatest number of pots with new growth, so the student concluded that soil type A was more effective that soil type B.

A biology student wanted to determine if using fertilizer would promote plant growth. One hundred plants were randomly assigned to one of two groups: one that used the fertilizer, and one that did not use a fertilizer.Which of the following is a benefit of having replication in the experiment?

A doctor wants to determine if a new medication for cholesterol is more effective than the previous medication. The doctor informs patients of a new medication and asks if they want to participate; 30 patients who are currently taking medication for cholesterol volunteer to be part of the study. She uses random assignment of the 30 patients to two treatment groups: one that uses the new medication, and one that uses the original medication. Which of the following describes the benefit of random assignment?

A teacher wanted to determine the effectiveness of two different learning tools—a computer program or a hands-on approach—for a particular concept she was preparing to teach. She will assign her students to one of the two methods to spend the whole class time to learn this concept.Which of the following variables would be moderated due to random assignment?

A doctor wants to determine if a new medication for cholesterol is more effective than the previous medication. The doctor informed a random selection of his patients of the new medication and asked them if they would like to participate in a drug trial to test the effectiveness of the new cholesterol medicine compared to the current medication. Twenty-five patients who were currently taking medication for cholesterol volunteered and were given the new medication. After two months, the patients’ cholesterol levels are checked.

A new cream was developed to reduce the irritation caused by poison ivy. To test the effectiveness, researchers put an ad online asking for volunteers to participate in the study. One hundred subjects replied, and they were informed that one group would receive the new cream and the other group would receive a cream with no active ingredient. All 100 subjects were exposed to poison ivy. Fifty were then assigned to the group with the new cream, and 50 were assigned to the group with the cream with no active ingredient. After three days, the subjects’ level of irritation was measured. The technicians who surveyed the subjects’ level of irritation as well as the subjects did not know which group received which treatment.

A company that manufactures golf balls produces a new type of ball that is supposed to travel significantly farther than the company’s previous golf ball. To determine this, 40 new-style golf balls and 40 original-style golf balls are randomly selected from the company’s production line on a specific day. The balls are then placed in a bag and shaken. A golf pro then selects a ball and hits it. The distance the ball travels is then measured. The bag is shaken again, and the golf pro selects another ball to hit. She continues this procedure until all 80 of the golf balls are hit.

A biology student wanted to determine if using fertilizer would promote plant growth. One hundred plants were randomly assigned to one of two groups as shown in the design web.Which of the following accurately describes the benefit of comparison in the experiment shown in the design web?