study quiz 3
Estelle's cornfield is divided into 666 regions. She wants to know if a new pesticide is as effective as the pesticide that she currently uses. She randomly assigns each of the 666 regions to either the new or current pesticide for a month, and she'll compare the effectiveness of the pesticides. What type of experiment design is this?
A completely randomized design
Researchers at Mississippi State University were studying the impact of different environmental sounds on ecosystems. For their study, they created 333 similar ecosystems in their lab containing a variety of insects and plants. They randomly assigned each ecosystem to be exposed to rock music, country music, or a conventional city soundscape for two consecutive weeks. At the end of the study, they measured how successful the species were in each ecosystem. What type of experiment design is this?
A completely randomized design
A certain disease is classified into 444 stages that distinguish how developed the disease is. Researchers studying a new potential treatment recruited over 100100100 patients with varying stages of the disease for their study. Half of the patients with stage 111 were randomly assigned to receive the new treatment, and other half of stage 111 patients received a placebo. A similar strategy was used for patients in each of the other stages. What type of experiment design is this?
A randomized block design with the stages as the blocks
An experiment involving a new pain relief medication involves subjects being randomly assigned to one of two treatment groups. Subjects in one group will take a daily dose of the new medication, and subjects in the other group will take an existing common pain medication. All subjects will check in with a doctor every week to report their symptoms and any side-effects. What does it mean for this experiment to be double-blind?
Both the subjects and the doctors are unaware of who is taking which medication.
Researchers working on a vaccine for HIV recruited over 16,00016,00016, comma, 000 volunteers for an experiment. Each volunteer was randomly assigned to receive monthly injections of either the vaccine or a placebo for a year. The researchers were curious if subjects who received the vaccine would be less likely to contract HIV than subjects who received the placebo. What does it mean for this experiment to be double-blind?
Both the subjects and the researchers are unaware of who is receiving the vaccine and who is receiving the placebo.
Karina wants to determine if kale consumption has an effect on blood pressure. She recruits 100100100 households and randomly assigns each household to either a kale-free diet plan or a kale-based diet. At the end of two months, she plans to record the original and final blood pressures for members of each household. PROBLEM 1 What is the explanatory variable?
Kale consumption
Researchers working on a vaccine for HIV recruited over 16,00016,00016, comma, 000 volunteers for a study. Each volunteer was randomly assigned to receive monthly injections of either the vaccine or a placebo for a year. The researchers were curious if subjects who received the vaccine would be less likely to contract HIV than subjects who received the placebo. What is the main reason for randomly assigning the subjects?
To create groups that are as similar as possible so the main difference between the groups is the treatment
Sadie is redesigning her company's website. She wants to carry out an experiment that involves randomly assigning visitors to either the existing design or the new design. A user's experience is slightly different depending on what type of device (mobile or desktop) they use, so Sadie wants to use a randomized block design. How should Sadie form the blocks?
Users within each block should use the same type of device as each other.
A company makes a bracelet that is designed to repel mosquitos so people don't have to wear bug spray. Researchers at the company are designing an experiment where volunteers will be assigned either the bracelet or bug spray to use at their homes. The researchers want to use a randomized block design. How should the researchers form the blocks?
Volunteers within each block should live in similar environments to each other when it comes to mosquitos.
A group of researchers wants to study the effect of listening to music at different volumes on driving reaction times. They recruit 100100100 volunteers. They assign each subject a number from 111 to 100100100 and use a random number generator to assign the first 505050 subjects selected to take the driving test with one music volume. The remaining 505050 subjects are assigned to take the test with the second music volume. What type of experiment design is this?
Completely randomized
A professor wants to study the effectiveness of a new study tool for a course. There are 150150150 students registered for the course. The professor assigns each student a number from 111 to 150150150 and uses a random number generator to assign the first 757575 students selected to use the new study tool. The remaining 757575 subjects are assigned to use the previous study tool. What type of experiment design is this?
Completely randomized
An online retailer wants to study whether more lenient return policies increase purchasing behaviors. They select a random sample of 200020002000 customers who have made purchases in the past year. They use a random number generator to select 100010001000 customer account numbers to assign to the treatment group. The remaining 100010001000 customers are assigned to the control group. What type of experiment design is this?
Completely randomized
Hilary recruits residents from her town who have physical exams scheduled in the next month with the local doctor's office. She randomly assigns the volunteers to either a Vitamin D supplement pill or a placebo pill. Participants do not know which pill they are taking. They have their blood pressures measured before the study begins and at the end of the study. Suppose Hilary finds that the group who took the Vitamin D supplements had a significant decrease in blood pressure, while the placebo group showed no significant change in blood pressure. PROBLEM A (SCENARIO 2) Based on this study, we can safely say this result probably holds true for:
Just the residents in Hilary's study.
A group of researchers wants to study the effect of listening to music at different volumes on driving reaction times. They recruit 100100100 volunteers. While music plays in the car at one of two volume levels, each subject encounters a number of signs, some of which require braking, and their reaction times are recorded. The subjects repeat the experiment at the other volume level. The order of the conditions is randomly assigned for each subject. What type of experiment design is this?
Matched pairs
A professor wants to study the effectiveness of a new study tool for a course. There are 150150150 students registered for the course. The professor ranks the students according to cumulative average in the prerequisite course. For every 222students, in order, from the list, the professor flips a coin to assign one student to use the new study tool and the other to use the previous study tool. What type of experiment design is this?
Matched pairs
An insurance company wants to study whether offering incentives for preventative care reduces overall health care costs. They select a random sample of 200200200 of their customers. The company ranks the customers according to total health care costs for the previous year. For every 222customers, in order, from the list, the insurance company randomly assigns one customer to be offered the incentive and the other to the control group. What type of experiment design is this?
Matched pairs
A survey of over 7,0007,0007, comma, 000 randomly selected employees in 151515 nations recently showed that employees who work in a digital workplace tended to be happier than those who don't work in a digital workplace. Can we conclude that working in a digital workplace caused employees to be happier? Why?
Not necessarily, because this wasn't an experiment
Researchers studying meditation contacted over 1,0001,0001, comma, 000 randomly selected adults in 101010 nations. The results showed that those who meditated on a regular basis were less likely to suffer from stress than adults who meditate less regularly or not at all. Can we conclude that meditating caused the lower stress? Why?
Not necessarily, because this wasn't an experiment
Alejandro owns a restaurant where he sells pizza by the slice. He wonders if customers prefer their pepperoni on top of the cheese or under the cheese. Every day for a week, he prepares both types of pizza. Every time a customer orders a slice of pepperoni pizza, he flips a coin to determine whether he'll give the customer a slice with pepperoni on top or under the cheese. He then asked each customer to rate their pizza. At the end of the week, he found that customers who received pepperoni on top rated their pizza significantly better on average than customers who received pepperoni under the cheese. What conclusion can they draw from this study?
Pepperoni placement caused the difference in customer ratings
A company wants to study the effectiveness of a new pain relief medicine. They recruit 100100100 volunteers who suffer chronic pain. Half of the 505050 males are randomly assigned to the treatment group, and the other half are assigned to the control group. The same method is used to randomly assign half of the 505050 females to the treatment group and the other half to the control group. What type of experiment design is this?
Randomized block
A professor wants to study the effectiveness of a new study tool for a course. There are 150150150 students registered for the course. Half of the freshmen are randomly assigned to use the new study tool, and the other half are assigned to use the previous study tool. The same method is used to randomly assign half of the sophomores, half of the juniors, and half of the seniors to each study tool. What type of experiment design is this?
Randomized block
A tutoring company has offices where students physically attend a test prep course. The company recently created an online test prep course, and they wonder if it produces similar or different outcomes than their in-person course. They recruit 505050 students who are willing to try the online course. On average, those 505050students produced significantly better outcomes than students historically do in the in-person course. The company concludes that the online course produced better outcomes than the in-person course for these students. Which of these concerns makes their conclusion inappropriate?
Some of the 505050 students should have been assigned to a control group that used in the in-person course.
Malaria is a disease spread by mosquitos. Researchers want to test a potential vaccine for the disease, so they plan on recruiting thousands of subjects from each of the 101010 countries that are most affected by the disease. The researchers want to use a randomized block design where some subjects receive the vaccine and the rest receive a placebo. How should the researchers form the blocks?
Subjects within each block should live in the same country as each other.
Researchers recruited participants for a wine tasting study that included a variety of wines in terms of style and price. The participants tasted a series of wines in a random order. Participants could look at the bottle for each wine so they could take its price and label information into account as they tasted and rated each wine. The participants rated the more expensive wines significantly better tasting than the less expensive wines. The researchers carrying out the study conclude that more expensive wines taste better. What is a confounding variable that makes their conclusion inappropriate?
The lack of blinding
Katie has 222 types of dog treats—chicken and beef—and she wonders which type her dog prefers. She carries out an experiment where she offers her dog both treats at the same time. For consistency, she always puts the chicken treat in her right hand and the beef treat in her left hand. Her dog chooses the chicken treat in 858585 of 100100100 attempts. Katie concludes that her dog prefers the chicken treats over the beef treats. What is a confounding variable that makes her conclusion inappropriate?
The lack of randomization in each attempt
Ricardo suspects that his cat will prefer a new cat food to their current cat food. For his cat's next feeding, he decides to feed his cat in a different room than usual. He puts a bowl of the new food on one side of the room and a bowl of the current food on the other side of the room (determined by a coin flip). His cat chooses the new food. Ricardo concludes that his cat prefers the new food to their current food. What makes Ricardo's conclusion inappropriate?
The lack of replication to other feedings
A gym that specializes in weight loss offers its members an optional dietary program for an extra fee. To study the effectiveness of the dietary program, a manager at the gym takes a random sample of 505050members who participate in the dietary program and 505050 members who don't. The manager finds that those who participated in the dietary program, on average, lost significantly more weight than those who didn't participate in the program in the past 333 months. The manager concludes that the dietary program caused the increased weight loss for the gym's members during that time period. What is a confounding variable that makes their conclusion inappropriate? Choose 1 answer:
The members' choice of whether or not they participated in the dietary program
An education researcher wonders if young students better learn arithmetic facts using physical flashcards or a new online game. The researcher recruits 505050 students for a study. The study allows parents to choose which learning tool they'd like their child to use: flashcards or the online game. Each student takes a pre-test and a post-test, and at the end of the study, students who used flashcards show significantly better outcomes than students who used the online game. The researcher concludes that flashcards were more effective than the online game for this group of students. What is a confounding variable that makes their conclusion inappropriate?
The parents' choice of which learning tool their child uses
A class was curious if their teacher could grade and return double-spaced papers faster than single-spaced papers. For a certain assignment, each student flipped a coin to determine if they would single-space or double-space their paper. The students agreed to all use the same font. The students who double-spaced received their graded papers back significantly faster than students who single-spaced. The class concluded that any teacher can grade and return papers faster if they are double-spaced rather than single-spaced. Why is their conclusion not appropriate?
The study was an experiment, but it didn't include anyone other than their teacher.
There is an ongoing debate about how many spaces should be placed after a period in typed documents. Alana read about a study where 100100100 participants all read the same document typed in Courier New font. Half of the participants were randomly assigned the document with one space after each period, and the other half were given the document with two spaces after each period. Participants who read the document with two spaces after each period were able to finish reading significantly faster than those with one space after each period. Alana concluded that using two spaces after each period will help people read all documents faster. Why is Alana's conclusion not appropriate?
The study was an experiment, but it didn't include fonts other than Courier New.
Diego read a medical research study about the connection between type 2 diabetes and walnut consumption. The study looked at dietary and disease patterns in a sample of over 30,00030,00030, comma, 000 American adults, and it found that those who consumed more walnuts were significantly less likely to have type 2 diabetes. Diego concluded that eating more walnuts would make him less likely to get type 2 diabetes. Why is Diego's conclusion not appropriate?
The study was observational, so he shouldn't make a causal conclusion.
Julia read about a study involving migraine headaches in men. The study of over 100100100 men found that those with migraines had higher estrogen levels, on average, than men who were migraine-free. Both groups of men had similar testosterone levels. Julia concluded that estrogen caused these men's migraines. Why is Julia's conclusion not appropriate?
The study was observational, so she shouldn't make a causal conclusion.
A surgeon developed a new procedure for knee replacement surgery. To study its effectiveness, they recruit patients who need knee replacement surgery and are willing to participate in a blind study. The surgeon randomly assigns each volunteer to receive either the new procedure or the standard procedure. After the surgeon performs the procedure, they monitor each patient to see if one group has better results than the other. What does it mean for this experiment to be blind?
The volunteers are unaware of which surgery they receive.
The superintendent of a large school district is curious about the relationship between students' grades and their participation in extracurricular activities. They take a random sample of 500500500 students and find that students with more participation in extracurricular activities are far more likely to have high grades than students with little or no participation. What conclusion can they draw from this study?
There was an association between extracurricular participation and grades, but it's not necessarily a causal relationship.
A footwear company wants to test the effectiveness of its new insoles designed to prevent shin splints resulting from running. They hire a group of physical trainers and a statistician, who recruits 100100100 healthy adults between the ages of 181818 and 242424 to participate in a study. The statistician randomly assigns 505050 of the adults to follow a weekly running schedule with the new insoles and the other 505050 to the same running schedule with the existing insoles the company already sells. After 101010 weeks, the statistician records the number of runners from each group that have developed shin splints. PROBLEM 1 What is the primary purpose of having a group of 505050 runners use the existing insoles?
They serve as a control group.
A team of psychologists was curious if omega-3 fatty acid supplements could help treat depression in adolescents. They recruited 505050 adolescents with varying levels of depression to participate in an experiment. The researchers randomly assigned each subject to take either an omega-3 supplement or a placebo daily, and they monitored subjects' depression levels throughout the study. What is the main reason for randomly assigning the subjects?
To create groups that are as similar as possible so the main difference between the groups is the treatment
Researchers recruited over 1,0001,0001, comma, 000 patients with chronic back pain to participate in a study about the benefits of acupuncture. Each subject was randomly assigned to one of these treatment plans: traditional Chinese acupuncture, placebo acupuncture, and conventional pain treatment (medication and physical therapy). What is the primary purpose of randomly assigning subjects to the different treatment plans?
To create groups that are as similar as possible so the main difference between the groups is the treatments
A car manufacturer created a new voice-control system that allows drivers to have limited use of their phones while keeping both hands on the wheel. They want to know if the system results in drivers making fewer mistakes, so they recruit volunteers for an experiment. Each subject is randomly assigned to one of three groups: voice-controlled phone use, regular phone use, or no phone use at all. Subjects drive the same simulated course while researchers send notifications at set moments to the drivers who can use phones. The researchers will then compare how many mistakes are made between the groups. What is the primary purpose of including a group who doesn't use a phone at all?
To serve as a control group for comparison
A company makes a bracelet containing magnets that they claim improves balance and overall athletic performance. Researchers recruit volunteers for an experiment. The subjects will test the effectiveness of the bracelet by performing a variety of athletic challenges with and without the bracelet. Each subject will do each challenge 333 times: wearing the actual bracelet, wearing a placebo bracelet, and wearing no bracelet at all. The order will be randomized for each activity, subjects won't know which bracelet is which. Why did the researchers include the scenario where subjects wear no bracelet at all?
To serve as a control group for comparison
Jillian has been updating the design of a media streaming website. She wonders if users will spend more time on the site with the new design, so she designs a study. She starts with a random sample of 1,0001,0001, comma, 000users and randomly assigns half of them to the old design and half of them to the new design. After a week, she notices that users with the new design spend significantly longer on the site than the users with the old design. Can we conclude that the new design caused users to spend more time on the site? Why?
Yes, because the users were randomly assigned to treatment and control groups
Hilary obtains a random sample of residents from her town. She surveys those residents on whether or not they consume Vitamin D and how much Vitamin D they get. She also measures their blood pressures. Suppose Hilary finds that among the people sampled, those who consume higher amounts of Vitamin D had significantly lower blood pressure than those who did not. PROBLEM A (SCENARIO 1) Based on this study, we can safely say this result probably holds true for:
all residents from hillarys town