Exam 4 Review HW & Quiz
Waiting time at a bus stop (in minutes) Qualitative or quantitative ?
Quantitative
Give examples of several forms of bias.
-A non-representative sample -An experiment that is not blinded -A researcher with a personal stake in the outcome distorts the true meaning of data
What is a placebo?
A placebo lacks the active ingredients of a treatment being tested in a study, but is identical in appearance to the treatment
Explain how populations & samples differ.
A population is a set of units of interest to a study. A sample is a subset of the units of a population.
What is a self-selected survey?
A survey where people decide for themselves whether to be part of the survey
Give an example of qualitative data & explain your reasoning.
An example is ratings of restaurants because they would be based on subjective opinions
What are three-dimensional graphics?
Are graphs that visualize data using images that look three dimensional
What is a bias & how can it affect a statistical study?
Bias refers to any problem in the design or conduct of a statistical study that tends to favor certain results
An exit poll designed to predict the winner of a local election uses voluntary surveys with every a Democrat who votes between 9-11am. What sources of bias, if any, might this study have?
Both selection & participation bias
A medical researcher randomly selects 500 Japanese & 500 American people and questions them. She finds that Americans work longer they're on average and also that they have a higher rate of heart disease. She concludes that working longer hours is associates with a higher incidence in heart disease. What is the biggest flaw in the study?
Confounding variables
What type of statistical study would give an answer to: Is magnetic therapy a more effective way to treat headaches than Drug A or doing nothing at all?
Experiment
In a study of the effects of magnets on back pain, some participants were treated with magnets while others were given no magnetic objects with a similar appearance. The magnets did not appear to be effective in treating back pain. Is this study observational or experimental?
Experimental— the treatment group is patients that used the magnets and the control group is patients that received the placebo Double blind
A double-blind drug versus placebo study of 101 patients suffering from tinnitus demonstrated the effectiveness of ginkgo biloba extract. The ginkgo treatment improves the condition of the tinnitus patients. Is this study observational or experimental?
Experimental— the treatment group is the patients that received the drug and the control group is patients that received the placebo Double blind
What type of statistical study would give an answer to: Does a certain garden fertilizer produce larger tomatoes?
Experiment— with treatment & control group
In a survey to assess attitudes toward genetically modified foods, which of the following questions will give the most accurate results?
How do you feel about genetically modified foods?
A researcher wishes to determine the level of support for a new environmental law. Which of the following questions will produce the most accurate results?
How do you feel about the new environmental law?
A cable network reports on a survey of America's top restaurants that found that "only mince restaurants achieved a rare 29/30 rating and none of those restaurants are in the Big Apple." What crucial information would you want to know before acting on this study?
How the quality of the restaurants was measured How the respondents were selected Who the respondents in the survey were
Why is it so important that a statistical study use a representative sample?
If the sample fairly represents the population as a whole, then it is reasonable to make inferences from the sample to the population
What problems can confounding variables cause?
Incorrect conclusions to be drawn form the study The study to favor certain results unexpectedly
How can making an experiment single-blind or double-blind help?
It an experiment is blinded, then any effect arising from psychological factors should affect all groups equally
In a class of 100 students, 47 students received a grade of B. What was the relative frequency of a B grade?
It was a 0.47 because the relative frequency of a category if the number of data values that fall in that category divided by the total number of data values.
Consider a study designed to learn about the school networks of all college freshman, in which researchers randomly interviewed students living in on-campus dorms. How will the study suffer due to the way this sample was chosen?
It will suffer from selection bias. Selecting students living in on-campus dorms may not accurately reflect the population
What are confounding variables?
Items or quantities that are not intended to be part of the study
In a surgery of 1002 people, 701 (71%) said that they voted in a particular presidential election. The margin of error for this survey was 3 percentage points. However, actual voting records show that only 60% of all eligible voters actually did vote. Does this imply they people lied when they responses in the survey?
Longer answer of the two ".....implying either that respondents intentionally lied to appear favorable to the pollsters or that their memories were inaccurate."
A researcher was interested in the exercise habits of the residents of the village of spine Heights. She interviewed every 10th person who left the post office until she had interviewed 100 people. Each of the people she interviewed was asked to rate their exercise level according to 1-5. The researcher reported that on average, they exercised moderately. What is the biggest flaw in the study?
Measurement of the variable is not well defined
As voters left various polls across the city, every tenth voter at edX polling station was asked who they had chosen to be the next mayor. What is the biggest flaw in the study?
No bias
A research group that tracks tuition rates at colleges and universities compares the tuition at a small college today and 10 years ago and claims that tuition has increased 150% during that period. Would you believe this claim?
No, since it is not clear whether inflation was taken into account
Citing a higher incidence of cell-phone-related accidents among teens, the governors office claims that banning the use of hand-held cell phones among drivers under 20 years of age will save lives. Would you believe this claim?
No, since the relationship between cell phone use and traffic fatalities is not described.
In my experimental study, I used a sample that was larger than the population. Does this statement make sense?
No, the statement does not make sense because a sample is a subset of the population and cannot be larger than the population.
The local Chamber of Commerce claims that the average number of employees among all businesses in town is 12.5 Is there reason to question the claim?
No, there is not reason. The Chamber of Commerce would have no reason to distort its data
What type of statistical study would give an answer to: Which team in a football league has the lineman with the greatest average weight?
Observational study
What type of statistical study would give an answer to: In a study done at a university, researchers took snapshots of 4500 white adults every four years for 24 years & determines that 9 out of 10 women will eventually become overweight.
Observational study; not case-control
A study at a university separated 106 volunteers into groups, based on psychological tests designed to determine how often they lied & cheated. Those with a tendency to lie had different brain structures than those who did not lie. Is this study observational or experimental?
Observational study— case control; the cases are the volunteers that had a tendency to lie and the controls are the volunteers that did not lie.
Imagine that a survey of randomly selected people finds that people who used sunscreen were more likely to have been sunburned in the past year. Which explanation for this result seems most likely?
People who use sunscreen are more likely to spend time in the sun
The marital status of individuals Qualitative or quantitative ?
Qualitative
The political affiliations of residentes of a city Qualitative or quantitative ?
Qualitative
The television shows being watched by households surveyed by a media research company Qualitative or quantitative & why?
Qualitative because they don't measure or count anything
The heights of subjects in a clinical trial of a new drug Qualitative or quantitative ?
Quantitative
The speed of a car in miles per hour Qualitative or quantitative ?
Quantitative
The weights of subjects in a clinical trial of a new drug Qualitative or quantitative ?
Quantitative
What is the distinction between qualitative & quantitative data?
Quantitative data describes categories (brand names & eye color), while quantitative data represent counts or measures (heights or quiz scores or students).
A film critic is interested in knowing which is the most popular film of the gear amongst Americans. To answer this question, he conducts a telephone poll in the NY metropolitan area & asks each person to name their favorite film of the year. What is the biggest flaw in the study?
Selection bias
From a poll of people who recently bought cold medicine at all stores of a large drugstore chain, investigators concluded that the mean time between colds for all Americans is 5.6 months. What sources of bias, if any, might this study have?
Selection bias only
In order to determine the opinions of people in the 18-26 year age group on controlling illegal immigration, researchers survey a random sample of 2500 National Guard members in this age group. What sources of bias, if any, might this study have?
Selection bias only
Members of a reproductive health service are surveyed to determine whether American adults prefer abstinence, counseling and education, or morning after pills for high school students. What sources of bias, if any, might this study have?
Selection bias only
A computer randomly selects 200 names from a list of all registered voters. Those selected are surveyed to predict who will win the election for Mayor. What type of sampling method is used?
Simple random sampling
Briefly describe four common sampling methods:
Simple random sampling Systematic sampling Convenience sampling Stratified sampling
A ___________ is obtained by dividing the population into homogenous groups & randomly selecting individuals from each group.
Stratified sample
An IRS auditor randomly selects for audits 30 taxpayers in each of the filing status categories: single, head of household, married filing jointly, and married filing separately. What type of sampling method is used?
Stratified sampling
To determine her heart rate, Charolette divides up her day into three parts: morning, afternoon & evening. She then measures her heart rate at 2 randomly selected times during each part of the day. What type of sampling method is used?
Stratified sampling
The government of a large city needs to determine whether the city's residents will support the addition of another fire house. The government decided to conduct a survey of a sample of the city's residents. Which one of the following procedures would be the most appropriate for obtaining a sample of the city's residents?
Survey a random sample of persons with each geographical region of the city
Consider an experiment designed to test whether cash incentives improve school attendance. The researcher chooses two groups of 100 high school students. She offers one group $10 for ever week of perfect attendance. She tells the other group that they are part of an experiment but does not give them any incentive. Is this experiment blind?
The experiment is not blind because the researcher & the students know which groups the students are in.
You want to determine the mean amount of credit card debt owned by adult consumers in Florida. Which sample is most likely to be a representative sample?
The first 1,000 Florida residents in a complete list of all Florida telephone numbers.
The headline "Drugs shown in 98% of movies" accompanied a news story that described a "government study" claiming that drug use, drinking or smoking was depicted in 98% of the top movie rentals. Discuss whether the headline accurately represents the story.
The headline refers to drugs whereas the story refers to "drug use, drinking or smoking". The headline is very misleading because the term "drugs" is generally considered to consist of drugs other than cigarettes or alcohols. Also, all movies consists of more than just the top movie rentals.
What do we mean by variables of interest in a study?
The items or quantities that the study seeks to measure
Describe the placebo effect & how it can make experiments difficult to interpret
The placebo effect refers to a situation in which a patient improves simply because they believe they are receiving a useful treatment. It can sometimes be difficult or impossible to distinguish between effects that arise from the actual treatment vs psychological factors
You conduct a poll in which you randomly select 958 registered voters from Texas and ask if they approve of the job their governed is doing. What is the population for this study?
The population is all the registered voters in the state of Texas because this is the entire group that is being selected from randomly
What is the purpose of binning?
The purpose of binning is to analyze the frequency of qualitative data grouped into categories that cover a range of possible values. A useful example is grouping quiz scores with a maximum score of 40 points with 10-point bins.
What is the difference between the following questions: -what percentage of Internet dates lead to marriage? -what percentage of marriages begin with Internet dates?
The questions have different populations
An article noted that chocolate is rich in flavonoids. The article reports that "regular consumption of foods rich in flavonoids may reduce the risk of Coronary Heart Disease." The study received funding from a candy company and a chocolate manufacturers association. Identify & explain any sources of bias in the study
The researchers may have been more included to provide favorable results because funding was provided by a party with a definite interest. The bias could have been avoided if the researchers were not paid by the candy company and the chocolate manufacturers
You read about an issue that was the subject of an observational study when clearly is should have been studied with a double-blind experiment. How can the results from the observational study be classified?
The results are essentially meaningless because there is no way to adjust the results to reflect what type of study should have been performed.
It can be said that a sample is representative of the population. What is meant by this?
The results found for the sample are similar to those we would expect to find for the entire population
A poll is conducted the day before a state election for Senator. There are only two candidates running for this office. The poll results show that 58% of the voters favor the Republican candidate, with a margin of error it 2 percentage points. Should the Republican expect to win?
The results suggest that the Republican is likely to win a solid majority because they will most likely get between 56-60%
Statistics is...
The science of collecting, organizing, & interpreting data and statistics are the data (numbers or other pieces of info) that describe or summarize something
A health researcher randomly selected 500 high school students from the city of Oak Grove. In a private interview the researchers asked the students whether they have ever used drugs. She concluded that only 8% of the high school students of Oak Grove have ever used drugs. What is the biggest flaw in the study?
The setting may discourage honest responses
A newspaper reports that over 60% of adults avoid visits to the dentist because of fear. What crucial information would you want to know before acting on this study?
The size of the sample The questions respondents were asked How respondents were chosen
A pharmaceutical company conducted a study to test the effectiveness of its new anti-depression medication. 500 adults suffering from depression were selected at random & were randomly assigned to either a treatment group or a placebo group. The experiment was double blind. The results were analyzed by the company. What is the biggest flaw in the study?
The source of the study
I was unable to make a bar chart because the data categories were qualitative rather than quantitative. Does this statement make sense?
The statement does not make sense because bar graphs are commonly used to show data when the categories are qualitative
My experiment proved beyond a doubt that vitamin C can reduce the severity of colds, because I controlled the experiment carefully for every possible confounding variable. Does the statement make sense?
The statement does not make sense because it is not always easy to discover the confounding variables.
My bar chart contains more information than yours because I made my bars 3D Does this statement make sense?
The statement does not make sense because making the bars 3D does not necessarily mean that information was added. It could mean that only the appearance of the graph was changed.
The TV survey got more than 1 million phone-in responses, so it is clearly more valid than the survey by the professional pollsters, based on interview with only few hundred people. Does the statement make sense?
The statement does not make sense because the 8 guidelines for evaluating a statistical study need to be reviewed before one study can be called more valid than another
I wanted to test the effects of vitamin C on colds, so I gave the treatment group vitamin C and the control group vitamin D. Does this statement make sense?
The statement does not make sense because the control group should only receive a placebo, not another treatment group.
The bar graph must be wrong, because your bars are wider than the ones shown on the teachers answer key. Does this statement make sense?
The statement does not make sense because the width of the bares in a bar graph does not affect the accuracy of the graph. As long as the width of the bars on your graph represent the same category or interval as the teachers graph and their heights are corresponding then your graph is also correct
T/F: a call-in poll on radio or TV is not reliable because the sample is not chosen randomly from a larger population
The statement is True because people choose to fall in. They are not randomly selected.
Your pie chart must be wrong because when I added the percentages on your wedges, they totaled 124% Does this statement make sense?
The statement makes sense because our charts are used primarily for relative frequencies, so the total pie must always represent the total relative frequency of 100%
There's been only a very slight rise in our stock price over the last few months, but I wanted to make it look dramatic so I started the vertical scale from the lowest price rather than from zero Does the statement make sense?
The statement makes sense because reducing the range of the vertical axis to just fit the data will increase the relative size of the variation in the data
The pre-election poll found that a candidate would get 42% of the vote, with a margin of error of 4%, but he still won the election. Does this statement make sense?
The statement makes sense because we can only be 95% confident that the actual percentage of people who vote for this candidate is between 38%-46%. There is still a chance that the actual percentage is more than 50%.
The relative frequency of B grades in our class was 0.3 Does this statement make sense?
The statement makes sense. Suppose there were 20 people in the class. If 6 received Bs, then the relative frequency of B grades was (6/20)= 0.3
The yes/no responses on a ballot initiative to the question "should casinos be allowed downtown?" Qualitative or quantitative ?
The variable is qualitative because yes/no responses on the ballot initiative are non-numerical categories
Suppose a researcher saw a placebo effect in an experiment to test a new treatment designed to cure warts. What did the researcher observe?
The watts of those in the control group were cured ever when using the placebo.
Consider an experiment in which the weights of 6 year olds were measure. What is the variable of interest in this study?
The weights of 6 year olds
Explain the difference between graphics that only appear 3D and those that show truly 3D data
Truly 3D graphics show data with 3 different variable plotted along 3 different axes. Graphics that only appear 3D show data with less than three different axes, but parts of it look 3D
According to a newspaper, 26% of Americans rate potatoes their favorite vegetable, making it the most popular vegetable. What crucial information would you want to know before acting on this study?
Were the respondents given the choice of potatoes or did they suggest it without a prompt How the question was asked How respondents were chosen
76% of those in the treatment group showed improvement 27% of those in the placebo group showed improvement Is there good evidence that the treatment is effective?
Yes
77% of those in the treatment group showed improvement 35% of those in the placebo group showed improvement Is there good evidence that the treatment is effective? Y/N?
Yes
A TV talk show host asks the TV audience, "Do you support new national mileage standards for automobiles?" and asks people to vote by a telephone at a toll-free number. Is there reason to question the results?
Yes, there is reason. 1) the TV audience might not be representative of the population 2) call-in polls tend to be biased 3) the wording of the question might produce inaccurate or dishonest responses
In a study designed to determine whether bicyclists who wear helmets have fewer accidents, researchers tracked 500 rides with helmets for one month. Is there reason to question the results?
Yes, there is reason. 1) the sample is biased; riders who do not use helmets should also be included
A study of the academic preparation of high school language arts teachers used the teachers' mathematics scores in a standardized test for data. Is there reason to question the results?
Yes, there is reason. 1) the variable that we're measured were not identified 2) scores on a standardized test do not necessarily predict preparation 3) the study was about the preparation of language arts teachers, but uses the teachers' mathematics scores
A study by a conservative foundation is designed to assess a new Democratic spending plan. Is there a reason to question the results?
Yes, there is reason. There is a possibility of bias in the study