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Andre is in the band and he is conducting an experiment to determine if high school students find listening to classical music or listening to the sounds of the ocean more calming. He selects five students at random from the band to listen to classical music. He then selects five people at random from the swim team to listen to the sounds of the ocean. What is problematic about the way that Andre selected his groups?
The participants were not randomly assigned into groups.
Jada is designing a study to determine whether mold grows faster in tap water or bottled water. To do this she compares the growth rate of mold growing in a glass of tap water to the growth rate of mold growing in a glass of bottled water.
a) What type of study is Jada designing?
b) How could her design be improved to collect data that would be better for answering the question of interest?
Experimental study.
Jada could use several different glasses of tap water and bottled water. Jada could make sure that the conditions, for example temperature and amount of sunlight, are the same for all of the glasses of water.
What type of study would you conduct if you wanted to know how many hours a week on average students at your school spend on homework? Explain your reasoning.
A survey could be used because you could ask students how many hours a week they spend on homework. A different type of observational study would be too difficult to track for many students. An experimental study would not be useful since the influence of one variable on another is not in question.
What is one major difference between an observational study and an experimental study?
Experimental studies directly influence something to see its effect, but observational studies do not directly influence the subjects.
Elena is conducting an experiment to determine if high school students are more relaxed when the lights are off or when music is played during an exam. She selects 10 of her friends to take an exam with the lights off and another 10 of her friends to take an exam with music playing. What is problematic about the way that Elena selected her groups?
The participants were not randomly assigned into groups. She only surveyed her friends and not all high school students.
You want to survey twenty of the 150 ninth graders to get their opinion on the school’s new schedule. Which of the following methods is most likely to lead to a sample that is the most representative of the 150 ninth graders? Explain how you know.
A: Choose 20 ninth graders from your first period class.
B: Choose the first 20 ninth graders from an alphabetical list.
C: Select 20 students at random from the ninth grade.
D: Select 5 students at random from each of ninth, tenth, eleventh and twelfth grade.
C
What type of study would you conduct if you wanted to know how many miles a week on average students on the school's cross country team run during the summer? Explain your reasoning.
A survey could be used because you could ask students on the cross country team how many miles a week they run during the summer. A different type of observational study would be too difficult to track for many students. An experimental study would not be useful since the influence of one variable on another is not in question.
Select all designs which describe an observational study that is not a survey. Explain how you know
A: 200 voters are randomly selected and asked how they will vote in the upcoming election.
B: 60 pieces of lumber are randomly selected. Half of those are randomly assigned to be treated with a new sealer. Three months later the level of rotting in all the pieces is recorded.
C: 100 pregnant women are randomly selected. For 8 weeks, the level of iron in their blood and their vital signs are recorded.
D: 400 incoming sixth grade students are randomly selected. Researchers record their results on a reading test at the beginning and end of the school year and compare the level of improvement seen in students at elementary schools to students at middle schools.
E: 300 people apply to test a new mattress. 100 of these customers are selected randomly to receive the new mattress and the others are given an older version. After 6 months they are asked to rate their satisfaction with the mattress.
C, E
Tyler is interested in how different environments affect dandelion plants. For a science fair project, Tyler looks for dandelions growing in the grass and growing in dirt without grass. He counts the number of days it takes each dandelion to turn from a yellow flower into seeds. After 6 weeks, he compares the number of days it takes for the dandelions growing in the grass to turn from a yellow flower into seeds to the number of days it takes for the dandelions growing in the dirt without grass to turn from a yellow flower into seeds.
a) What type of study is Tyler designing?
b) How could his design be improved to collect data that would be better for answering the question of interest?
a) Observational study
b) Tyler could design an experimental study and compare dandelions grown in the same conditions, except one group grows with grass and another without grass.
The United States Senate has 2 senators from each of the 50 states. Select all methods that would select a sample of 10 senators at random from the entire Senate. Explain how you know.
A: Take the 10 senators from the 5 largest states.
B: Take the 10 senators who have served in the Senate the longest.
C: Place the names of all 100 senators on individual slips of paper placed into a bowl. Thoroughly mix up the slips and then select 10 of them.
D: Send letters to all 100 senators. Select the 10 that reply back the quickest.
E: Number the senators from 1 to 100. Use a random number generator to make a list of 10 random integers between 1 and 100 inclusive.
C, E
Describe the design of an experimental study that could determine whether you send text messages faster before or after exercise.
Assign 50 students to a group that types a 160 character text message before and after running for 5 minutes. Assign 50 students to a group that types a 160 character text message before and after watching a 5 minute video. Record how long it takes students to type the 160 character text message before and after the running or watching the video.
In an observational study, it was noticed that people that eat more chocolate tend to have better blood flow than the general population. Researchers wonder whether the improved blood flow might be caused by flavanols (a molecule found in many foods). Dark chocolate contains a high concentration of flavanols, but milk chocolate contains a much lower concentration.
How could the researchers design an experiment to determine the effects of flavanol on blood flow from the different types of chocolate?
The researchers could get people to participate in an experiment where they are randomly assigned to eat either a set amount of dark chocolate or milk chocolate daily for a week. Their blood flow can then be measured.
For physics class, Jada wants to know how the surface of different ramps affects the maximum speed of a marble being rolled down the ramp. To study this, she compares the maximum speed of a marble rolled down ramps with different surfaces. She rolls the same marble down each type of ramp 10 times.
What type of study is this? Explain how you know.
Experimental study