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A reporter for the university newspaper wants to find out the opinions that all BYU students have about the university health center. During a class break, he goes to the health center, contacts a few students as they exit and asks them to fill out a survey. What type of survey is this?
This is a convenience sample and does not involve the use of a random device to select the patients. Every health center patient does NOT have a probability of being selected.
In a random digit telephone survey, homeless people or people with only cell phones do not have telephones that can be called with random digit dialing. What type of bias is this?
Since these people cannot be contacted, under-coverage bias will result.
Suppose a survey is so long that many respondents refuse to complete it. What type of bias could result?
These respondents are “not responding” to the questions at the end of the survey. This is called non-response bias.
Which of the following describes a valid sampling procedure?
A valid sample is any sample selected using some type of random device that gives every member of the population “a chance” of being selected. Examples include simple random sample, stratified sample and multistage sample.
True or false: Taking a valid simple random sample eliminates all biases, including question wording bias and interviewer bias.
We cannot eliminate all bias even with a simple random sample. Non-response, and response bias such as question wording and interviewer bias are always possible. (A valid simple random sample at least eliminates bias that results from not using a random device.) We just do the best we can to keep bias as low as possible.
Select a simple random sample of three people from the following population of 8 people. Begin on the left of random digits and use them in the order given. Use the numbering for the people as given.
1. Adams 2. Garcia 3. Powell 4. Rathgerber 5. Bowden 6. Ling 7. Thurmin 8. Winkler
Random digits: 82297 15102 56027 55892 33063 41842 81868 71035
What are the names of your sample in the order they were selected?
True or false: We can establish causation whenever a valid simple random sample is taken.
Even though a valid random sample is taken, causation conclusions can be made only when an experiment is performed. This is due to potential confounding variables in observational studies which include random samples.
What is type of study is this?
Since parents were randomly chosen from within each race, this is a stratified sample.
Since parents are sampled from the school, the population is all parents of Black, White and Hispanic high school students. Opinions of the parents are the measurements or results on the parents, but not the population.
Parents were randomly selected from within each race. So, the sample is those parents of Black, White and Hispanic high school students who were surveyed.
On August 27, 1995 an article in the Los Angeles Times reported that in its survey of 3297 California adults, 2780, or 83.4% had health insurance coverage. These results have a margin of error of plus or minus 1.4%. What is the population of interest?
The population is the entire group of individuals about which the researcher is interested. In this example, Californian adults were surveyed, so the population is all Californian adults. The 3297 Californian adults were the sample. Those with health coverage are a subset of the population.
The correct answer is: All adults living in California
On August 27, 1995 an article in the Los Angeles Times reported that in its survey of 3297 California adults, 2780, or 83.4% had health insurance coverage. These results have a margin of error of plus or minus 1.4%.
What variable is being measured on each individual?
The variable is the measurement or characteristic recorded on each individual. In this survey, each adult was asked whether they had health insurance coverage. So, the variable is whether an adult has health insurance coverage. NOTE: the variable is what is measured on EACH individual.
The correct answer is: Whether an adult has health coverage
On August 27, 1995 an article in the Los Angeles Times reported that in its survey of 3297 California adults, 2780, or 83.4% had health insurance coverage. These results have a margin of error of plus or minus 1.4%. What type of study is being described?
A study is an experiment if the researcher deliberately imposes a treatment on the individuals; a study is an observational study if the researcher merely observes and records information about individuals. In this study, the researcher asked whether the adult had health insurance coverage and recorded their answer. No treatment was imposed. So, this is an observational study. Surveys are always observational studies.
The correct answer is: an observational study.
A computer manufacturer has just received a shipment of 8000 computer chips. In order to insure that shipment meets their quality standards, they want to sample a few chips and make a detailed examination of the sample. The chips are packaged individually and have serial numbers. If they use a statistical software package to select serial numbers for 20 chips for inspection, what type of sampling is this?
Since 20 chips are selected from the entire group of 8000 chips, this is a simple random sample.
The correct answer is: A simple random sample.
The college of humanities in a large university was accused of discrimination in their faculty hiring. Twenty records of the recent female applicants who weren't hired and twenty records of the recent male applicants who weren't hired were randomly selected and compared with the records of the recent hires. What type of sampling design is this?
The twenty records of female applicants who weren't hired were selected separately from the twenty records for male applicants who weren't hired. Sampling was done within the female applicants and within the male applicants. That makes this stratified sampling.
The correct answer is: A stratified sample.
What is the advantage of performing an experiment over conducting an observational study?
Because the researcher imposes a treatment on each individual in the study and measures the response, the researcher can use the results to establish whether the treatments "cause" changes in the response. By the way, experiments are more likely to be unethical than observational studies.
The correct answer is: The results of an experiment can be used to establish causation.
What type of bias results when people respond differently to questions asked by male interviewers than they do to questions asked by female interviewers?
Because the bias results from "gender" of the interviewers, we call this "interviewer bias."
The correct answer is: Response bias due to interviewer effect
True or false: Undercoverage bias usually exists in non-probability samples.
Consider taking a convenience sample by contacting students in the school cafeteria. Students who are too busy to hang out in the school cafeteria cannot be contacted and will be part of the under-coverage. The survey results will be especially biased if you ask a question such as "How many hours do you work per week?"
The correct answer is: True
You are planning a report on apartment living in a college town. You decide to select three apartment complexes at random for in-depth interviews with residents. Use the random numbers below 38167 98532 62183 70632 23417 26185 41448 75532
to select a simple random sample of three of the following apartment complexes. Label them in alphabetical order beginning from 01. Note: Answers are given in alphabetical order, not in order of selection. (List of names didn't fit on flash card)
Take digits two at a time. Begin by skipping 38 as it was not assigned. The first unassigned two digit number is 16 which corresponds to "Fairington." 79 and 85 were not assigned. 32 corresponds to "Waterford Court." 62 was not assigned. 18 corresponds to "Fowler." So the three apartment complexes are Fairington, Fowler, Waterford Court.
Here are the two questions differing only in uses suggested for the remaining surplus: "Should the money be used for a tax cut, or should it be used to fund new government programs?" "Should the money be used for a tax cut, or should it be spent on programs for education, the environment, health care, crime-fighting and military defense?" One of these questions drew 60% favoring a tax cut. The other drew only 22% favoring a tax cut. Which wording pulls more respondents toward a tax cut?
Because the wording of the first question does not elaborate on governmental uses for the money, a tax cut sounds more appealing so respondents are more likely to select a tax cut. The wording of the second question gives valid uses for a tax cut that appeal to most adults so fewer would select a tax cut.
The correct answer is: The first wording biases respondents towards a tax cut because it does not elaborate on the possible uses of the surplus.
A state department of employment security notes that last year 68% of people who filed claims for unemployment insurance found a new job within 15 weeks. As an incentive to find a job, the state offers $500 to people filing unemployment claims if they find a job within 15 weeks. The percent who do so increases to 77%. Why does confounding with lurking variables make it impossible to say whether offering $500 really caused the increase?
Lurking variables could account for the increase in the percent of unemployment insurance applicants who find a job in 15 weeks. These could include things such as differences in the types of people who filed claims for unemployment or an upturn in the economy coinciding with the program's onset which resulted in an increase in job availability. That's why it is impossible to say that the treatment really caused the increase in unemployed who found work in 15 weeks.
A major difference between an observational study and an experiment is that an observational study does not have an explanatory variable with treatment levels.
A major difference between an observational study and an experiment is that in an observational study the subjects (or someone like their guardian or doctor) chooses their treatments, but in an experiment the treatments are randomly assigned to the subjects.
Both an observational study and an experiment can have an explantory variable with treatment levels.
Why is the principle of control/comparison so important in an experiment?
By randomly allocate subjects into two or more groups, the characteristics of a potential lurking variable are distributed evenly in these groups. This will neutralize the effect of the potential lurking variable. Further, we cannot measure treatment differences unless we have two or more treatment groups.
Which one of the following is a benefit of randomized block designs (RBD)?
Randomize block designs remove variation associated with the blocking variable from the measure of overall experimental variation. This gives more precise estimates of chance variation which helps in determining whether results are statistically significant.
Here is a stem plot of the breaking strength of wood, rounded to the nearest hundred pounds. What is the largest value in this data set? Note that the leaf unit = 100. This means that 1:1 is 1100 or 21:1 is 21,100.Variable: LoadLeaf unit = 100.0
The largest stem is 33. The last number on this line is “7”. Since “leaf unit = 100.0”, this “7” is read “700”. So the largest number of 337 is written as 33700.
True or false: Statisticians prefer the median over the mean even when outliers are present in the data.
True or false: The mean is affected by every value in a data set.
Jane, a student at BYU, decides to study opinions of BYU students concerning grading in religionclasses. She obtains a roll from every religion class and randomly selects five students on each roll.This is an example of
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