Q1:-What is the response variable?

race and sex

doctors from the American College of Physicians or the American Academy of Family Physicians

cardiac catheterization and coronary bypass

Q2:-Researchers at the University of Wisconsin at Madison conducted an experiment to study the effect of meditation on the immune system. The researchers randomly assigned volunteers to one of two treatments. One group completed an 8-week course in meditation and actively practiced meditation during this period. The other group received no meditation training and did not meditate during the 8-week period.

At the end of the experiment researchers gave the subjects a flu shot. A healthy immune system will produce antibodies in response to a vaccine. At 4-weeks and 8-weeks after the flu shot, researchers did a blood test to measure the levels of antibodies produced against the vaccine. Both groups had an increased level of antibodies, but the meditators had a significantly greater increase in antibodies than the non-meditators. Psychosomatic Medicinepublished the results in 2003 in an article titled "Alterations in Brain and Immune Function Produced by Mindfulness Meditation."

Stress can harm the immune system. So stress could be a confounding factor in this experiment. Which of the following features of the experiment design is the best way to control the effects of stress on the results of the experiment?

use volunteers (people who have time to volunteer for a study are probably not stressed out by a busy life)

use random assignment to treatment groups

Q3:-The authors of the paper "Action-Video-Game Alters the Spatial Resolution of Vision," (Psychological Science[2007]:88-94) concluded that spatial resolution, an important aspect of vision, is improved by playing action video games. They based this conclusion on an experiment in which 32 volunteers who had not played action video games were "equally and randomly divided between the experimental and control groups." Subjects in each group played a video game for 30 hours over a period of 6 weeks. Those in the experimental group played Unreal Tournament 2004, an action video game. Those in the control group played Tetris, a game that does not require the user to process multiple objects at once.

Based on this description of the experiment, which control is part of the experiment design? Check all that apply.

a control group

random assignment

direct control

Q4:-In its January 25, 2012, issue, the Journal of the American Medical Association (JAMA) reported on the effects of overconsumption of low, normal, and high protein diets on weight gain, energy expenditure, and body composition. Researchers conducted a single blind, randomized controlled trial of 25 U.S. adults. All subjects were admitted to the inpatient metabolic unit for the duration of the trial (10 to 12 weeks). The subjects were healthy, weight-stable, male and female volunteers, aged 18 to 35 years. All subjects consumed a weight-stabilizing diet for 13 to 25 days. Afterwards, the researchers randomly assigned participants to diets containing various percentages of energy from protein: 5% (low protein), 15% (normal protein), or 25% (high protein). The subjects were not aware of the specific protein level diet to which they were assigned. On these diets the researchers overfed the participants during the last 8 weeks of their 10 to 12 week stay in the inpatient metabolic unit.

Which of the following is used in the design of this experiment? Check all that apply.

Control group

Incorrect. In an experiment, the control group is the group that does not receive treatment by the researchers. A control group is used as a benchmark to compare the outcome(s) for the groups receiving treatment.

Blinding of subjects

Correct. The subjects were not aware of the specific protein level diet to which they were assigned.

Blinding of reserachers.

Direct control of confounding variables

Correct. In addition to random assignment, researcher in this experiment took additional steps to directly control for the effects of confounding variables. For example, to control the diet of each subject, all subjects consumed a weight-stabilizing diet for 13 to 25 days prior to being assigned to one of three treatment conditions (low, normal, or high protein).

Random assignment

Correct. The researchers randomly assigned the subjects to one of the three treatment groups (low protein, normal protein, high protein).

Q5:-

Researchers randomly divide participants into groups. Each group takes a different amount of omega-3 fatty acid supplements daily for a month. One group receives a placebo. The researchers measure the impact on cholesterol levels in the blood.

What is the purpose of random assignment in this experiment?Check all that apply.

To ensure that all people with high cholesterol have an equal chance of being selected for the study

To increase the accuracy of the research results and prevent skewness in the data

To produce treatment groups with similar characteristics

Correct. Random assignment uses chance to create similar treatment groups.

To control confounding

Q6:- Label each study as either an observational study, an experiment, or neither.

For years doctors have used a laser to drill holes in the hearts of patients with severe untreatable angina (chest pain). Many patients have reported a lasting and dramatic decrease in chest pain after undergoing the laser procedure. Doctors have never fully understood why the laser procedure works to relieve angina. Martin Leon, MD, at Lenox Hill Hospital in New York led a randomized trial to test the effectiveness of this laser procedure. The trial consisted of 500 patients with severe untreatable angina across 25 clinics. The patients were randomly assigned to either the laser treatment or a placebo. The surgical procedures were identical. Patients were sedated but awake and a small incision was made in the skin. During the procedure, the patient could hear the surgeons discussing the laser process and see projections with elaborate visual effects of the patient's heart. Each patient was convinced that the surgery was real. The placebo worked as well as the real laser procedure. "There was absolutely no difference," says lead investigator Dr. Leon. Leon made his presentation at the Transcatheter Cardiovascular Therapeutics 2000 international meeting.

In this study, the researchers impose treatments on the subjects - the placebo surgery where no hole was drilled in the heart, or the laser surgery where a hole was drilled in the heart.

A 2007 U.S. study by Fontana, Klein, and Holloszy compared a number of factors associated with heart disease and metabolic disorders such as diabetes and blood pressure. Three groups of twenty-one participants in this study were matched for age, gender and other characteristics. The subjects in the raw vegan diet group were sedentary and had been eating a low-calorie, low-protein vegan diet composed primarily of unprocessed and uncooked plant-derived foods for at least 2 years. The subjects in the endurance runners group ran an average of 48 miles per week for an average of 21 years. The subjects in the western diet group consisted of sedentary and non-obese subjects who ate a typical western diet (characterized by high intakes of red meat, sugary treats, high-fat foods, and refined grains). All subjects in the study were healthy adults. Results of this study were published in the American Journal of Clinical Nutrition in 2006.

In this study, researchers do not impose a treatment on the subjects in any of the three groups. Each of the three types of diets and exercise routines were self-imposed by the subjects before the study began.

Many parents have expressed concerns that pertussis vaccinations will cause wheezing disorders or asthma in later life. In 2009 the Journal of the American Academy of Pediatrics published research by the Institute of Social and Preventive Medicine in Bern, Switzerland. The researchers wanted to determine if routine childhood vaccination against pertussis (whooping cough) was associated with subsequent development of childhood wheezing disorders and asthma. The researchers studied 6811 children from the general population born between 1993 and 1997 in Leicestershire, UK. From birth through 2003, they conducted repeated questionnaire surveys about wheeze and asthma and then linked the respiratory symptom data to independently collected vaccination data from the National Health Service database. Then the researchers compared wheeze and asthma incidents for children of three different levels of vaccination (complete, partial, and no vaccination). The analyses were based on 6,048 children with available vaccination records.

Q7:-Chemicals in butter-flavoring: Workers in a microwave popcorn production plant in Missouri breathe chemicals that are part of the butter-flavoring. Are these workers at greater risk of developing lung problems? To investigate this question, 135 workers at the plant receive a survey, and 117 respond.

Researchers want to compare workers in the popcorn production area with workers who have jobs in other parts of the plant. People in these other jobs are not directly exposed to the butter flavorings. Of the 97 workers in the production area, 30 reported experiences of "shortness of breath." Of the 20 workers in other jobs, only 1 reported "shortness of breath."

What can we conclude from this study? Check all that apply.

Since only 117 of the 135 workers in the plant participated in the survey, we must use caution when drawing conclusions.

Incorrect. Approximately 87% of workers responded to the survey. This is very high response rate to a survey.

Exposure to the chemicals in butter-flavoring is associated with a greater incidence of lung problems, such as shortness of breath.

The chemicals in the butter-flavorings are causing shortness of breath because a much larger percentage of workers in the production area have shortness of breath.

Workers exposed to the chemicals in the butter-flavoring have a higher risk of developing respiratory problems such as shortness of breath.

Correct. The word "risk" implies an association or relationship between the explanatory and response variables. This is appropriate for an observational study.

Q8:- Traffic Safety:Here is a passage from a study published by the National Highway Traffic Safety Administration in 2007.

"The National Occupant Protection Use Survey (NOPUS) is the only probability-based survey of driver cell phone use in the United States. The survey observes usage as it actually occurs at a random selection of roadway sites, and so provides the best tracking of the extent to which people in this country are using cell phones while driving."

NOPUS observed 43,000 drivers in this study.

To identify the population and the sample for this study, label each item on the left with a term on the right. Note - any given term on the right may be used more than once or not at all.

Drivers in the United States

Neither

This is the group the researchers were interested in learning about.

Drivers in the United States who use cell phones while driving

Sample

Researchers observed drivers and noted whether the driver was or was not using a cell phone. Using a cell phone is the response variable with two categories -using a cell phoneandnot using cell phone.

The 43,000 drivers observed in the study

Population

This is the group that the researchers gathered information from.

Q9:- Pumpkin patch: Suppose we plant pumpkins in a garden where half of the plants are shaded. Then, to test a new fertilizer, we fertilize the plants in full sun and do not fertilize the plants in the shade. In the fall the fertilized plants yield more, bigger, and prettier pumpkins.

To identify the explanatory and response variables, match each of the following with one of the terms on the right. Note - any given term may be used more than once or not at all.

Fall season

The researchers are not studying the impact of the fall season on the pumpkin harvest.

Fertilizer

Pumpkin harvest

Amount of sunshine

Q10:- The Hawthorne Works was a large Western Electric factory with 45,000 employees. During the 1920s and 1930s Hawthorne Works was the site of some well-known industrial studies. In one of the studies, researchers investigated the impact of different working conditions on worker productivity. Prior to the start of the study, researchers secretly measured workers' productivity for several weeks. Then researchers chose two workers, who then chose their own teams. The teams were separated from the general workforce and completed their work in different experiment rooms where the researchers could observe them more easily. Over a 5-year period researchers manipulated the structure of the workday for each team (number and duration of breaks and number of hours per shift). For each of these changes in working conditions, the researchers measured the effect on productivity. For some conditions, such as frequent short breaks, workers rebelled by intentionally decreasing productivity.

Which of the following features is used in the design of this experiment? Check all that apply.

Single blinding

Incorrect. The subjects in this study were aware that the researchers manipulated their working conditions.

In a single blind study, the subjects are blinded to prevent their preferences or expectations from affecting the outcomes. This way the subjects' preferences or expectations do not become confounding variables. In fact, the subjects in this experiment deliberately introduced a confounding variable. They disliked taking six 5-minutes breaks. So they deliberately reduced output in order to end the breaks.

Random assignment

Incorrect. The researchers did the opposite of random assignment. They asked each test-group leader to choose four other female workers to join her test group. Additionally, at least one of the listed design features was used in this experiment.

Control group

Correct. A control group is a group that receives no new treatment. The control group provides a baseline for comparison. To establish the baseline, researchers secretly measured the output of telephone relays two weeks before manipulating the women's working conditions. Thus, the women were their own control group.

Direct control of confounding variables

Incorrect. The design of this experiment did not include direct controls for confounding variables. In fact, the researchers allowed the subjects to introduce confounding variables. For example the test workers disliked having six five-minute breaks. So they deliberately reduced output in order to end the breaks.

Treatment group

Correct. The treatments were the number and duration of breaks during the workday. The researchers applied these treatments to the two test groups. So the test groups were the treatment groups.

Q11:-In spring 2014, faculty from the City University of New York (CUNY) reported on a randomized controlled trial they conducted. The goal of the experiment was to determine whether community college students who assess into elementary algebra could be successful if they were placed directly into college-level statistics (with extra support). The experiment was conducted at three urban CUNY community colleges. At the time of their recruitment into the experiment, participants did not plan to major in a subject requiring college algebra. Students who assessed into elementary algebra and agreed to participate in the study were randomly assigned to one of three treatments: 1) traditional elementary algebra, 2) traditional elementary algebra with extra support in a weekly workshop, or 3) college-level statistics with extra support in a weekly workshop.

To control for teacher effects, each faculty member in the study taught one section associated with each of the 3 treatments. All of the instructors were full-time math faculty, and at each of the three colleges, there were four sections of each treatment for a total of 36 sections across the colleges with 721 student participants. In a comparison of course pass rates (C or better), students placed directly into college-level statistics outperformed both elementary algebra treatment groups.

Which of the following is an example of direct control in this experiment? Check all that apply.

Optional participation in the study for students who assess into elementary algebra

Incorrect. Optional participation in the study could affect the success rates for each of the three groups of courses. Perhaps students needing the most algebra review opted not to participate in the study. The study design could not ethically control for this unwanted effect.

Conducting the experiment at three different community colleges

Correct. The community college could affect the success rates for each of the three groups of courses. Perhaps one college offers more support services than another college. The study design controlled for this by conducting the experiment at three different community colleges.

Each instructor teaches one section of each of the three courses

Correct. The instructor could affect the success rates for each of the three groups of courses. Perhaps one instructor is an easier grader than another instructor. The study design controlled for this by requiring each participating instructor to teach one section of each of the three courses.

Q12:-What is the purpose of random assignment in an experiment? Check all that apply.

To select a sample that is representative of the population

Incorrect. Researchers use random selection to obtain a sample that is representative of the population.

To create similar treatment groups

Correct. The goal of random assignment is to produce treatment groups with similar characteristics. If the groups are similar, then any differences we see in the response variable are due to the differences in the treatments.

To eliminate the effects of the explanatory variable

To control voluntary response bias

Control for confounding variables

Correct. Random assignment is used to control the effects of confounding variables. By controlling confounding variables, random assignment provides evidence of a cause-and-effect relationship between the explanatory and response variables (as opposed to a cause-and-effect relationship between a confounding variable and the response variable).