Stat 121 quiz 2
A couple plans to have three children. There are eight possible arrangements of girls and boys. For example, GGB means the first two children are girls and the third child is a boy. All eight arrangements are (approximately) equally likely. Write down all eight arrangements of the sexes of three children. Based on the eight arrangements, what is the probability of any one of these arrangements? - 0.0833 - 0.100 - 0.125 - 0.250 - 0.375 - 0.500
0.125
A shoe manufacturer wanted to determine which type of material, "Material X" or "Material Y", to use on the soles of their shoes to get maximum wear. Twenty teenage boys wore one shoe with each type of sole. For each young man, a coin was tossed; if heads, "Material X" would go on the right shoe and "Material Y" on the left. If tails, "Material X" would go on the left shoe and "Material Y" on the right. After wearing these shoes for four months, the thickness of the sole of each shoe was measured. What type of study is this? -A randomized controlled experiment. -A simple random sample. -A voluntary response sample. -A matched pairs experiment.
A matched pairs experiment
To test the effectiveness of using a dab of honey to prevent infection in a cut, parents of children in a childcare facility were instructed to wash the wounds of their children with soap and water and then place a dab of honey on the cut. Each cut was then monitored for infection. At the end of the study, the percentage of cuts that became infected was computed. Why is this NOT a valid experiment? There is no randomization. There is no blinding - parents may use more care and those monitoring for infection may be less stringent in their diagnosis. -There is no control group that gets a placebo for comparison. -Parents may be more careful of the cuts of their children since they know they are in an experiment. -The results may not apply to all children since only those children in a day care facility participated. -All of these answers are correct.
All of these answers are correct.
What does the distribution of a random variable give us? -The measure of the amount of deviation of the random variable about the mean. -A density curve whose x values are always positive. -All possible values of the random variable and how often they occur.
All possible values of the random variable and how often they occur.
What is the advantage of an experiment over an observational study? -An experiment can be used to establish causation. -Inference can only be made on experimental results. -The results of an experiment will not be biased. -The explanatory variable will not be confounded with a -lurking variable.
An experiment can be used to establish causation.
Students at a particular university are able to evaluate professors on a five point scale (a score of 1 meaning poor teaching and a score of 5 meaning excellent teaching). What type of random variable is professor evaluation an example of? -Discrete -Continuous -It is impossible to say given the information provided.
Discrete
R.A. Fisher, a famous statistician, describes a well-known design in his book, Design of Experiments. Five varieties of wheat were compared to determine which gave the highest yield in bushels per acre. Eight farms were available for planting. Each farm was divided into five plots. For each farm, the five varieties were randomly assigned to the five plots with one variety per plot. The varieties were planted on their assigned plots and their yields were measured and compared. What type of study is this? -Observational study - multistage sample -Experiment - randomized block design -Experiment - randomized controlled experiment -Observational study - simple random sample -Observational study - stratified sample
Experiment - randomized block design
True or False: A prospective observational study is when researchers collect data from past records and do not follow up on patients.
False
True or False: A study is an observational study when the researchers randomly assign treatments to the subjects.
False
True or False: We can establish causation whenever a valid sample (simple random sample, stratified sample, multistage sample, etc.) is taken.
False
In studies of worker productivity, it has been noticed that any change in the work environment together with the knowledge that a study is underway will produce a short-term increase in productivity. This is known as -placebo effect. -Hawthorne effect. -lack of realism. -non-compliance.
Hawthorne effect.
An educational software company wants to compare the effectiveness of its computer animation for teaching about supply and demand curves with that of a textbook presentation. The company tests the economic knowledge of a number of first-year college students, then randomly divides them into two groups. One group uses the animation, and the other studies the text. The company retests all the students and compares the increase in economic understanding in the groups. Is the study described above an experiment? Why or why not? -It is not an experiment because there is no attempt to influence the responses on the tests on economic understanding. -It is not an experiment because it does deliberately impose a condition on the first-year college students. -It is an experiment because it only measures students' economic knowledge. -It is an experiment because the students were randomly assigned to either the animation group or the textbook group.
It is an experiment because the students were randomly assigned to either the animation group or the textbook group.
Medical experiments are often double blind in nature. What does this mean? -The subjects in the control group receive a placebo treatment. -Neither the subject nor the person evaluating the subject (the doctor or nurse) knows which treatment the subject receives. -All data on individuals are kept confidential -Subjects are randomly assigned to treatments without the doctor's knowing how the randomizing was done.
Neither the subject nor the person evaluating the subject (the doctor or nurse) knows which treatment the subject receives.
Researchers want to determine if there is a link between whether an individual uses illegal drugs and whether they graduated from high school. They randomly survey 300 people and asked them following questions: "Did you graduate from high school?" "Have you ever used illegal drugs?" What type of study is this? -Observational Study -Randomized Comparative Experiment -Matched Pairs Experiment -Randomized Block Experiment
Observational Study
To investigate the effects of the drug phen-fen, 200 women in the 30-40 age range who had used the drug for at least one year were located. 200 women of the same age group who had not used the drug were also located. The incidence of heart valve abnormality was compared between the two groups. What type of study is this? -Observational Study -Randomized Controlled Experiment -Randomized Block Experiment -Matched Pairs Experiement
Observational Study
A study followed adults for three months to determine if certain foods resulted in better wellbeing. Study participants were required to keep a log of the foods they ate during the three months. Additionally, at the end of each day, study subjects were required to rate their mood, physical aches and pains, and energy levels. What type of study is this? Prospective observational study Retrospective observational study Survey Experiment
Prospective observational study
Which one of the following is a benefit of randomized block designs (RBD)? -RBD eliminates all lurking variables. -RBD reduces chance variation by removing variation associated with the blocking variable. -RBD removes bias. -RBD eliminates the placebo effect.
RBD reduces chance variation by removing variation associated with the blocking variable.
Researchers want to compare the effectiveness of exercise and dieting compared to dieting alone for weight loss. They have 60 volunteers, 30 men and 30 women. They randomly assign half of the men to Group 1, exercise and diet, and the other half to Group 2, diet alone. They follow the same procedure for the women. Half of the women are assigned to Group 1 and the other half are assigned to Group 2. After 16 weeks, their weight loss was measured and compared. What type of study is this? -Observational Study -Randomized Controlled Experiment -Matched Pairs Experiment -Randomized Block Experiment
Randomized Block Experiment
Because of concerns about employee obesity and related health problems, a very large company conducted a study to compare two weight-reducing programs (low-carb diet and low-fat diet). Forty employees volunteered to participate in the study for a 10-week period. Half of the employees were randomly assigned to the low-carb diet and the other half randomly assigned to the low-fat diet. What type of study is this? Observational Study Randomized Controlled Experiment Randomized Block Experiment Matched Pairs Experiment
Randomized Controlled Experiment
What is the major difference between an observational study and an experiment? -Subjects choose their treatment in an experiment. -Researchers assign treatments to subjects in an experiment. -Experiments frequently have confounding between two variables in their effect on the response variabl
Researchers assign treatments to subjects in an experiment. In an experiment we choose the treatment that each subject gets. Whereas with an observational study, the subject have already chosen their "treatment" and we are just observing what is already going on.
What type of bias results when people respond differently to questions asked by male interviewers than they do to questions asked by female interviewers? -Undercoverage bias -Nonresponse bias -Response bias due to respondent lying or deliberately giving incorrect information -Response bias due to question wording -Response bias due to interviewer effect
Response bias due to interviewer effect
Reserachers use car crash data to determine how many crashes were related to driver distraction in the past year. What type of study is this? Prospective observational study Retrospective observational study Survey Experiment
Retrospective observational study Survey
What is the advantage of performing an experiment over conducting an observational study? The results of an experiment do not have any bias. Experiments are easier to perform than observational studies. Experiments are not as likely to be unethical. The results of an experiment can be used to establish causation.
The results of an experiment can be used to establish causation.
What is a correct description of the median of a distribution that is described by a density curve? The value in the data set that occurs with the highest frequency. -The point that is intermediate between interquartile range and standard deviation. -The value that divides the area of the density curve in half. -The point at which the distribution "balances".
The value that divides the area of the density curve in half.
True or False: Performing an experiment allows us to establish causation.
True
True or False: The placebo effect happens when patients improve because they believe they are receiving the treatment when they may not be receiving the treatment.
True
True or False: Two variables are said to be confounded when their effects on the response variable cannot be distinguished from each other.
True
True or False: Observational studies of the effect of one variable on another often fail because the explanatory variable is confounded with lurking variables.
True This statement is true. Observational studies typically have lurking variables in them because there was no random assignment of treatments.
When are two variables said to be confounded? When both have the same effect on the response variable. When their effects on the response variable cannot be distinguished from each other. When both variables are explanatory variables. When both variables are treatment variables.
When their effects on the response variable cannot be distinguished from each other.
