7. Additional Principles of Experimental Design (Quiz)

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? Having a large number of plants receiving the treatments will allow for a good comparison of the differences in plant growth between the two groups. Having a large number of plants receiving the treatments will not allow for a good comparison of the differences in plant growth between the two groups. Replication is not needed in this experiment. One plant receiving each type of treatment is enough to determine if the difference in plant growth is due to the fertilizer. Repeating the experiment will allow the student to compare the differences between the plants that received the fertilizer the first time and the plants that received the fertilizer the second time.

a.

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 received fertilizer, and one that did not receive fertilizer. Which of the following statements is true about the benefits of random assignment? The variability between each plant may not be evenly distributed between the two groups, so any observed differences in the plant growth between the two groups would not be due to the fertilizer. The variability between each plant would be evenly distributed between the two groups, so any observed differences in the plant growth between the two groups are more likely due to the fertilizer. The variability between each plant may not be evenly distributed between the two groups, so any observed differences in the plant growth between the two groups may or may not be due to the fertilizer. The variability between each plant would be evenly distributed between the two groups, so any observed differences in the plant growth between the two groups are guaranteed to be due to the fertilizer.

b.

A new cream was developed to reduce the irritation caused by poison ivy. To test the effectiveness, researchers placed 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. Which of the following is a benefit of having replication in the experiment? Repeating the experiment will allow the researchers to compare the differences between the subjects that received the new cream both times. Having a large number of subjects receiving the treatments will allow for a good comparison of the differences in level of irritation between the two groups. Having a large number of subjects receiving the treatments will not allow for a good comparison of the differences in level of irritation between the two groups. Replication is not needed in this experiment. One subject for each type of treatment is enough to determine if the reduction in level of irritation is due to the new cream.

b.

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. What type of experiment is this? single blind double blind placebo effect controlled experiment

b.

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. Of the 50 subjects that were assigned to the cream with no active ingredient, 15 stated they had less irritation. What is this called? placebo control group placebo effect placebo control

c.

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. Is this a valid conclusion? Yes, because the leaves were randomly assigned, this evenly distributed the variability in the leaves; therefore, type A soil is more effective than type B soil. Yes, because the amount of water and light were controlled, this may have reduced the variability in the response; therefore, type A soil is more effective than type B soil. No, because the pots with type A soil were closest to the window, they received more light, which may have led to the new growth. No, because only African violets were used, replication was not properly implemented; therefore, we cannot conclude that type A soil was more effective.

c.

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. Which of the following is a true statement concerning the use of a placebo? The placebo is given to one group of subjects to see if the subjects receiving the placebo experience fewer allergic symptoms than the subjects taking the new medication. The placebo is given to one group of subjects to see if the subjects receiving the placebo experience more allergic symptoms than the subjects taking the new medication. The placebo is given to one group of subjects to see if the subjects receiving the placebo think they have fewer allergic symptoms because they believe they are taking the new medication. The placebo is given to one group of subjects to see if the subjects receiving the new medication think they have fewer allergic symptoms because they believe they are taking the new medication.

c.

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? There is no need for comparison in this experiment. The overall growth of the plants can be compared to see which plants benefit the most from fertilizer. The growth of the plants in the treatment group only can be compared to see if the fertilizer had a significant effect. The growth of plants in the treatment group and the control group can be compared to see if the fertilizer had a significant effect.

d.

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. Has the principle of comparison been addressed in this experimental design? Yes, because the balls are randomly selected, the distances of the new ball can be compared to the distances of the original ball. Yes, because the original ball type is included in this experiment, the distances the different balls travel can be accurately compared. No, because a placebo ball was not used, a comparison cannot be made to determine if the new ball travels significantly farther. No, because all of the new type of balls are not hit first, the distances they travel cannot be compared to the distances of the original ball.

not a.

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? the teacher time spent in class computer experience the different learning tools

not d.