STATS 121
By what time do you need to start a midterm exam on the last day it is offered?
4 PM In the Exams section of the syllabus it says "The last midterm test is handed out at 4:00 PM on the last day."
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 sample is this?
A convenience sample A convenience sample is a sample where the researcher contacts those subjects who are readily available and does not use any random selection. The results are almost surely biased.
Educators in California are concerned about a recent newspaper article reporting that students in the United States are falling behind students in other nations in their math skills. They decide to sample 10th grade students throughout the state and test their mathematics skills. They first randomly select 10 school districts. From each of these 10 school districts they randomly select three high schools. From these 3 high schools they randomly select 10 students and test them. What type of sample is this?
A multistage sample A multi-stage sample is sampling is conducted in stages; for a two-stage sample, the individuals are grouped according to some characteristic— groups are first randomly selected and then individuals are randomly selected from those selected groups. (In a stratified sample, individuals are randomly selected from every group.) For example, states could be randomly selected; then school districts within selected states, followed by schools within selected school districts within selected states and finally students would be randomly selected from the selected schools from the selected school districts from selected states. That would be a four-stage sample
A large university in the western United States wants to survey the faculty regarding its plan to combine the spring and summer terms into one semester. It randomly selects 5 colleges on its campus and from each of these colleges, randomly selects 4 departments. Within the chosen departments, 4 faculty members are selected to be included in the sample. What type of sampling design is this?
A multistage sample. This is a multistage sample because we are taking samples in multiple levels. Level one is when we sample 5 colleges and level 2 is when we sample 4 departments within each college that we samles. So it's a sample within a sample.
A high school teacher wants more information about her students' study habits. She writes each of her students' names on an identical slip of paper and places them in a hat. After mixing up the papers, she selects 30 students from the hat. She then asks the question, "How many hours a week do you study outside of school, 0-3, 4-6, or more than six?" and records their responses. What type of sample is this?
A simple random sample A simple random sample is a sample of size n selected from the population in such a way that each possible sample of size n has an equal chance of being selected.
A computer manufacturer has just received a shipment of 8000 computer chips. In order to ensure that the 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 randomly select serial numbers for 20 chips for inspection, what type of sampling is this?
A simple random sample. This is a simple random sample because each chip has an equal probability of being selected, it's like a draw from a hat. There is no grouping before we sampled so it's not a stratified sample. We are randomly selecting our sample so it is not a convenience sample. And there are not multiple levels of sampling so it is not a multistage sample.
Suppose a researcher is interested in the average ACT score for high school students in Illinois. She randomly selects 20 counties and then randomly selects 3 high schools from each selected county and then asks each student in the selected high schools what their ACT score was. What kind of sample is this?
A stratified sample Stratified sample is a sampling scheme where the population has been divided into stratum according to some characteristic and a simple random sample is selected from within each stratum.
The college of humanities in a large university was accused of discrimination in their faculty hiring. Twenty records of the recent female applicants who were not hired and twenty records of recent male applicants who were not hired were randomly selected and compared with the records of the recent hires. What type of sampling design is this?
A stratified sample. This is a stratified sample because we are first spliting the population into two groups: male and female. Then within each of those groups we take a sample and we compare the results. They key part is that we split the population into groups then took samples
A television station is interested in predicting whether or not voters are in favor of an increase in the state sales tax. It asks its viewers to phone in and indicate whether they support or are opposed to the proposed increase in order to generate additional revenue for education. What type of sampling design is this?
A voluntary response sample. This is a voluntary response sample because it is up to the viewers to make the phone call and become a part of the sample. We didn't choose those who participated in the study, the participants made that choice.
When can you see the correct answers for each Credit Quiz?
After 11:00pm on its due date (except for this quiz, which shows immediately so that you can know which questions you missed and try again if needed)
We sometimes hear that marriage is good for your career. A sample of 8235 managers and professionals employed by a specific large manufacturing firm were asked their marital status (married, single, widowed, or divorced) and their annual income. The mean annual income was then calculated for each of the four marital status groups. What is the population? what is the sample?
All managers and professionals employed by this manufacturing firm. Our sample comes from our population so if the sample was taken from managers and professionals employed by a specific large manufacturing firm, then that will be our population. The 8235 managers and professionals from this large manufacturing firm.
Which of the following potentially allows researchers to establish that the treatments "cause" changes in the responses?
An experiment We can only determine causation if a experiment is performed.
What is the advantage of an experiment over an observational study?
An experiment can be used to establish causation. We can have inference in an experiment and an observational study as long as we have randomization either by random selection or random allocation. Experiments can still be biased, and there can still be confounding in an experiment.
Which of the following describes confounding? A. A condition where the effect of one variable on the response variable changes depending on the level of another variable. B. A condition where the effect of one variable on the response variable cannot be separated from the effect of another variable. C. A condition where the effect of one treatment on the response variable is different from the effect of another treatment on the response variable.
B. A condition where the effect of one variable on the response variable cannot be separated from the effect of another variable.
Which of the following is a categorical variable? A. Height B. Phone Number C. Mile time D. Book costs
B. Phone Number
Which of the following describes a valid sampling procedure? A. Interviewer uses a set of personal criteria to pick respondents B. Respondents are chosen by an impersonal chance device C. Each respondent chooses whether or not to respond D. The first 50 people at a shopping mall are selected 7
B. Respondents are chosen by an impersonal chance device For valid sampling, subjects need to be chosen at random.
How can you earn extra credit in Stat 121?
By answering iClicker questions in class for up to 2% extra credit for overall course grade. Under the iClicker quizzes section of the syllabus it says "At least one quiz will be given sometime during each class and can add up to 2% extra credit points to your overall course grade."
Which of the following is NOT a valid probability sample? A. A simple random sample B. A stratified sample C. A multistage sample D. A voluntary response sample
D. A voluntary response sample Probability samples include an element of randomness, they are simple random samples, stratified samples, cluster samples, and multistage samples. Non-probability samples are volunteer samples, convenience samples and quota samples.
Late Exams (after the exam has closed) will be subject to which of the following penalties? A. 20% score reduction for the first day B. 10% score reduction each additional day C. $10 fee D. All of the above
D. All of the above
Statistics is a process where we do which of the following? A. Collect data B. Summarize data C. Interpret data D. All of the above
D. All of the above Big Picture of Statistics: 1 producing data, 2 exploratory data analysis, 3 probability, 4 inference
Why might collecting data from a sample be preferred over collecting data from a population? A. Less expensive. B. Less time consuming. C. Collecting data from the entire population may be impossible. D. All of the above.
D. All of the above. CMU eBook page 5 says: "In most cases the population is so large that as much as we want to, there is absolutely no way we can study all of it. A more practical approach would be to examine and collect data from a sub-group of the population, which we call a sample."
Which one of the following is NOT a consequence of lack of randomization? A. Results could be biased B. A lurking variable is likely confounded with the explanatory variable C. Laws of probability cannot be used to measure uncertainty in conclusions D. Not enough individuals will be available to measure chance variation
D. Not enough individuals will be available to measure chance variation Not having enough people has nothing to do with randomization 9
Which of the following is not part of the Big Picture of Statistics? A. Collecting data. B. Summarizing data. C. Interpreting data. D. Publishing research results.
D. Publishing research results. We're never required to publish our results to the public.
Which one of the following statements is true regarding credit quiz and writing assignment scores? A. The four lowest credit quiz scores will be dropped from grade calculations with no exceptions. B. The four lowest credit quiz scores will be dropped from grade calculations except Credit Quiz 00, Credit Quiz 01 and Writing Assignment 2. C. The four lowest credit quiz scores will be dropped from grade calculations except Writing Assignment 1. D. The four lowest scores will be dropped from grade calculations except Credit Quiz 01 and both writing assignments.
D. The four lowest scores will be dropped from grade calculations except Credit Quiz 01 and both writing assignments. Under the Credit quizzes and writing assignments section of the syllabus, it says that the four lowest quiz scores will be dropped at the end of the semester, except for Credit quiz 1 and the writing assignments.
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? A. There is no randomization. B. There is no blinding - parents may use more care and those monitoring for infection may be less stringent in their diagnosis. C. There is no control group that gets a placebo for comparison. D. Parents may be more careful of the cuts of their children since they know they are in an experiment. E. All of these answers are correct.
E. All of these answers are correct.
Four of the following express potential problems to the study described in question 3, but one is NOT a potential problem. Which one of the following is NOT a potential problem? A. Amount of hair on the subject's arm may affect degree of pain B. Results may be biased because there is not blinding of subjects as to when they receive which treatment. C. The study was not double blind. In fact, it was not even single blind. D. Subjects may already prefer one method of removal over another, so results may be biased. E. The study lacks realism because the subjects can't tell how each band-aid is removed.
E. The study lacks realism because the subjects can't tell how each band-aid is removed. The more hair on your arm the more ripping off a bandaid will hurt, there was no blinding so subjects knew which treatment they were receiving, growing up you've had lots of band aids and may have a preferrd method. But the study does NOT lack realism because the subjects can tell how the bandage was removed.
Is the right hand generally stronger than the left in right-handed people? You can crudely measure hand strength by placing a bathroom scale on a shelf with the end protruding, then squeezing the scale between the thumb below and the four fingers above it. The reading of the scale shows the force exerted. Which of the following best describes the design of a matched pairs experiment to compare the strength of the right and left hands using 10 right-handed people as subjects?
Each subject squeezes the scale twice: once with his right hand and once with his left hand with the order randomly determined. Scale readings are then compared.
A study of computer-assisted learning examined the learning of "Blissymbols" by children. Blissymbols are pictographs (think of Egyptian hieroglyphs) that are sometimes used to help learning-impaired children communicate. The researcher designed two computer lessons that taught the same content using the same examples. One lesson required the children to interact with the material, while in the other the children controlled only the pace of the lesson. Call these two styles "Active" and "Passive", respectively. Children were assigned at random to Active and Passive groups. After the lesson, the computer presented a quiz that asked the children to identify 56 Blissymbols. What type of study is this?
Experiment
Two hundred twenty-eight children in a study were assigned to one of three groups. Group one was required to consume 5 mg of caffeine or less each day, Group two was required to consume 5-20 mg of caffeine a day, and Group three was required to consume more than 20 mg of caffeine per day. At the end of three weeks, their parents reported the average amount of sleep their child got each night. What type of study is this?
Experiment Experiment, because the subjects were assigned treatments.
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? Was using the eight farms as blocks appropriate? How was randomization incorporated into this study?
Experiment - randomized block design Yes, because it removes lurking variables from farm to farm. All five varieties were randomly assigned to the five plots at each farm.
True or False: Convenience sampling is a type of probability sampling design.
False
True or False: We can establish causation whenever a valid sample (simple random sample, stratified sample, multistage sample, etc.) is taken.
False
True or False: The Field of Statistics starts when we begin summarizing data.
False Big Picture of Statistics: 1 producing data, 2 exploratory data analysis, 3 probablity, 4 inference
True or False: We can establish causation whenever a random sample is taken.
False False, because we can have a random sample but do a observational study. Where we can only determine causation from experiments.
True or False: There is no deadline for iClicker, CMU eBook, and LaunchPad eBook registrations.
False False. Refer to the syllabus for the deadline for iClicker, CMU eBook, and LaunchPad eBook registration.
True or False: In an experiment, subjects choose their treatment.
False In an experiment subjects are always assigned treatments.
True or False: The statistical term population can only refer to people.
False The population is the group we are interested in.
True or False: Taking a valid simple random sample eliminates all biases, including question wording bias and interviewer bias.
False There are other types of bias besides sampling bias, such as response bias, question wording bias, interviewer bias, etc.
Where can you get detailed information about CMU eBook, LaunchPad eBook, and iClicker registration?
From "Getting Started" under the Content tab of Learning Suite.
Where can you find the writing assignment instructions?
From Learning Suite. In the Credit quizzes and writing assignments section of the syllabus it says "Details for these writing assignments are found on Learning Suite under the Content tab."
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
Hawthorne effect.
Which type of graphical display is used for large sets of quantitative data?
Histogram
Which graph is not used to display quantitative data?
Histogram Histograms and stemplots are used to visualize quantitative data. Pie charts can be used to categorical data but a bar graph is the preferred way.
What is the final step in the Big Picture of statistics, as outlined in class?
Inference The four steps in the Big Picture of statistics are: 1. Producing Data 2. Exploratory Data Analysis 3. Probability 4. Inference
What is a sample?
It is a subgroup of the population. Definition of a sample
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 an experiment because the students were randomly assigned to either the animation group or the textbook group.
What does the statistical term "population" refer to?
It refers to the group we want to study or learn something about. CMU eBook page 5 says: "The process of statistics starts when we identify what group we want to study or learn something about. We call this group the population."
Gas mileage was compared for Premium and Regular gas for twenty Toyota Prius's. Each car was run on a tank of Premium gas and on a tank of Regular gas. Before the study, a coin was tossed for each car. If the coin was heads, the car was first tested with Premium gas; if the coin was tails, the car was first tested with Regular gas. At the end of the study, average miles per gallon for the two types of gas was compared. What type of study is this?
Matched Pairs Experiment Match Pairs Experiment is a type of experiment in which each subject receives both treatments in a random order, or the subjects are matched in pairs as closely as possible, and one subject in each pair receives each treatment. In this experiment each car will get both treatments.
High school students are selected by choosing at random several of the city's high schools and then randomly selecting some of the students from those selected high schools. What sampling technique is being used?
Multistage sampling. In this study we are taking a random sample of groups, those groups being a high school. Then within each high school we select we are taking another random sample of students. This is an example of multistage sampling with two stages
Medical experiments are often double blind in nature. What does this mean?
Neither the subject nor the person evaluating the subject (the doctor or nurse) knows which treatment the subject receives.
Does ripping off a band-aid hurt less than slowly pulling it off? Researchers plan to compare the two methods by applying two medium sized band-aids to the underside of the right forearm of each of 50 volunteer subjects. One band-aid will be randomly selected to be pulled off with a quick yank while the other will be gently peeled off. The order in which the band-aids are removed will also be randomized. After each band-aid is removed, the subject will be asked, "On a scale of 0 to 10, how much did the removal hurt?--with zero for "no pain" and 10 for "the worst pain imaginable." Does this study incorporate the principle of double-blinding? what is the explanatory variable? Does it incorporate randomization?
No, because the researchers and the subjects knew which treatment they were getting Double blinding is when neither the subject nor the doctor, nurse or whomever is diagnosing the results knows which treatment the subject received. In this case the researcher and the subject both knew which treatment was being received so double blinding was not incorporated. Method of band-aid removal The explanatory variable is a phrase that describes all possible treatments, in this case the treatments were having the bandage removed slow or fast. So we can describe that as band aid removal method. Yes, both the order in which the band-aids were removed and which band-aid was removed with which treatment were randomized. Randomization as a condition can be met by random selection (ex. SRS) or random allocation. In this problem random allocation was incorporated as both the order in which the bandages were removed and which band-aid was removed with which treatment were randomized.
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
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? Why might the results from the study above be biased?
Observational Study People may not want to admit they have used illegals drugs, resulting in response bias.
On August 27, 1995, an article in the Los Angeles Times reported that in its survey of 3297 California adults, 2780 (83.4%) had health insurance coverage. These results have a margin of error of ± 1.4%. What type of study is being described?
Observational study
Two hundred twenty-eight surveyed parents reported the amount of caffeine their 8 to 12 year old children consumed on a typical day. They also gave the average time their children slept each night. The purpose of the study was to determine whether amount of caffeine consumed affected how much children 8 to 12 years old sleep. What type of study is this? what is a potential lurking variable? A. Sugar content: Children may consume caffeinated beverages that also contain sugar, which could affect their sleep patterns. B. Time of day: Caffeine consumed in the morning may have less effect on sleep patterns than caffeine consumed at night. C. Age: Older children may be less affected by caffeine than younger children. D. All of the above
Observational study The children were not assigned to how much caffeine they should in take. All of the above Sugar content will because different sodas have different amounts of sugar and the more sugar you intake can affect how much you sleep. Time of day the caffeine is consumed will effect the study because if the child is drinking soda in the morning when they go to sleep that night they soda will have already gone through their system, where if they drink the soda right before bed it will have a stronger effect on their sleep. Age will also because older children are less affected by caffeine than younger children.
To determine whether there is a relationship between amount of time spent commuting to work each day and overall job satisfaction, a researcher surveyed 100 people that commute to work and asked them to report the average number of minutes they spent commuting to and from work each day during the previous week and rate their job satisfaction on a scale from 1 to 10. What is the response variable in this example?
Overall job satisfaction The response variable is their overall job satisfaction because that is how they are responding to their commute time.
Patients often show improvement even when they get a sugar pill from a doctor rather than the actual medication. What is this phenomenon called?
Placebo effect The placebo effect is when the response of patients to any treatment even though it has no physical effect. Where the Hawthorne Effect is a phenomenon whereby people in a study behave differently from how they would normally behave because they are being observed.
What is the first step in the Big Picture of Statistics?
Producing Data Big Picture of Statitics: 1 producing data, 2 exploratory data analysis, 3 probablity, 4 inference
In an email survey, students were asked, "During the past week, how many nights did you go to sleep past midnight?" What type of variable is "number of nights going to sleep past midnight"?
Quantitative
Administrators at Cosmo University are becoming more and more alarmed at the number of hours students work per week. In order to examine the relationship between the number of hours worked per week in a semester and that semester's GPA, one administrator surveyed 300 students currently attending the university. What type of variable is the number of hours worked per week?what type of variable is GPA?
Quantitative The number of hours worked per week is a quantitative variable (a variable with meaningful numerical values). Quantitative GPA is a quantitative variable (a variable with meaningful numerical values).
What type of data are displayed in stemplots, dotplots, and histograms?
Quantitative data These are all ways to display quatitative data. Pie charts and bar graphs are ways to display categorical data.
Consider the following two survey questions: Question 1: How satisfied are you with your current job: very satisfied, somewhat satisfied, somewhat dissatisfied, very dissatisfied? Question 2: What do you think can be improved about your job?
Question 1 is a closed question and Question 2 is an open question
Consider the following two survey questions: Question 1: How often do you read a book for fun (outside of work or school)? Question 2: How often do you read a book for fun (outside of work or school): never, sometimes, or often? Are these examples of open or closed questions?
Question 1 is an open question and Question 2 is a closed question.
Which one of the following is a benefit of randomized block designs (RBD)?
RBD reduces chance variation by removing variation associated with the blocking variable. Randomized block design because we sort subjects into blocks based on looking variables we can reduce the chance variation associated with that 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?
Randomized Block Experiment A randomized block design is when the sampled subjects are split into blocks based upon different values of a background or lurking variable and then randomly allocated treatments within each block. In this experiment they blocked on gender.
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?
Randomized Controlled Experiment
A study was conducted to test the effectiveness of using an antidepressant called imipramine in treating bulimia, an eating disorder. Twenty patients were randomly assigned to one of two groups with ten in each. One group received imipramine and the other received a placebo. The response measured was binge frequency. What type of study is this?
Randomized Controlled Experiment A Randomized controlled Experiment is an experimental design where all individuals participating in the experiment are assigned at random to the treatments. In this experiment each patient was randomly assigned to receive imipramine or a placebo.
What is the major difference between an observational study and an experiment?
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?
Response bias due to interviewer effect
What is an advantage of using a stem and leaf plot, rather than a histogram?
Stem plots can show exact values, where histograms are more approximate
The nonprofit group Public Agenda conducted telephone interviews with parents of high school children. Interviewers chose equal numbers of black, white, and Hispanic parents by randomly selecting from within each race using student records. One question asked was "Are the high schools in your state doing an excellent, good, fair, or poor job, or do you not know enough to say?" What type of sample is this?
Stratified sample Stratified sample is a sampling scheme where the population has been divided into stratum (race) according to some characteristic and a simple random sample is selected from within each stratum (race).
A study of religious practices among college students interviewed a sample of 127 students; 107 of the students said that they prayed at least once in a while. Which of the following best describes the sample?
The 127 college students who were interviewed. We're studying the religious practices among all college students, not just those who are already doing religious practices.
When registering your iClicker, if you cannot read your "Remote ID" number on the back at the bottom of your iClicker, where should you go to find obtain that number?
The Help Desk in the Textbook Department of the BYU Bookstore.
Two hundred twenty-eight children in a study were assigned to one of three groups. Group one was required to consume 5 mg of caffeine or less each day, Group two was required to consume 5-20 mg of caffeine a day, and Group three was required to consume more than 20 mg of caffeine per day. At the end of three weeks, their parents reported the average amount of sleep their child got each night. What is the explanatory variable?
The amount of caffeine a child got each day.
Because more questions about statistics have been added to the state exam, a school district decided to add a probability-statistics unit to their ninth-grade general mathematics course. To determine whether the unit will have an impact on scores on the state exam, all ninth-grade students enrolled in a general mathematics course in the largest high school in the school district were randomly allocated into two groups. One group of 281 students received instruction in a new probability and statistics unit in addition to the traditional instruction; the other group of 311 students received only traditional instruction. Students in both groups were given the state exam at the end of ninth grade to determine whether the group receiving additional instruction in probability and statistics had a higher average score than the group receiving just traditional instruction. What is the explanatory variable in this study? Who are the subjects in this study? Does the study described incorporate the principle of randomization? Does this study incorporate the principle of control or comparison? Does the study described incorporate the principle of replication?
The type of general mathematics instruction received: new instruction or traditional instruction. Ninth-grade students enrolled in a general mathematics course. Yes, because we are told that "students . . . were randomly allocated . . ." Yes, because the group of students receiving only traditional instruction can be considered a control or comparison group. The group of students receiving the additional instruction of probability-statistics can be considered the active treatment group. Yes, because there were 281 students in one group and 311 in the other group (more than one individual per treatment group)
What is the purpose of statistics?
To convert data into useful information. CMU eBook page 5: "what statistics is all about is converting data into useful information."
An experiment that doesn't incorporate randomization is NOT a valid experiment. T or F?
True
If images in a Credit Quiz are not showing up on your computer, you can download the PDF version of the images for each credit quiz from Learning Suite > Content > Quiz PDFs. T/F?
True
True or False: Inference is the way that we are allowed to draw conclusions about the population based on the data collected about the sample.
True
True or False: No late credit quizzes or writing assignments will be accepted.
True
True or False: The placebo effect happens when subjects improve because they have confidence in the medical provider and hope in the medication, even when they may not be receiving the treatment.
True
When we use a randomized block design we want the subjects within each "block" to be similar but they should be different from block to block.
True
A sample of 12th-grade students who took the National Assessment of Education Progress year 2000 mathematics test had a mean score of 250. Referring to the previous question, the variable test scores is quantitative. (t/f?) What is the population?
True all 12th-grade students who took the National Assessment of Educational Progress year 2000 mathematics test The purpose of this study was to determine the effect of adding a unit to the district's math course would have on the scores of the state exam. This study was done with a sample of ninth-grade students who were enrolled in a general mathematics course.
True or False: A randomized block design should be used when the subjects within groups (called blocks) are similar in ways that affect the response variable, but different from one block to the next.
True A randomized block design is when the sampled subjects are split into blocks based upon different values of a background or lurking variable and then randomly allocated treatments within each block.
True or False: All statistical summaries and conclusions should be reported in context.
True If statisical results were reported out of context what would they tell us? We need to report them in context to be able to understand the data.
True or False: Without random selection, we cannot appropriately apply the laws of probability to perform inference.
True The sample will only apply to the population that it represents. For example, if we took a sample of students in just section 23 of stat 121, then our results would only represent that section and not the whole class. However, if we took a random sample that included students from all of the sections, this would represent the whole class.
True or False: Cause and effect relationships cannot be established from observational studies because the explanatory variable is usually 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.
In a random digit telephone survey, neither people who are homeless nor people who only own a cell phone have land-line telephones that can be called with random digit dialing. What type of bias is this?
Undercoverage bias
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?
Undercoverage bias Because all those people without phones will be missed in our study, our study is not truly representative of the whole population and is biased. Undercoverage bias, is when not every subject in your population of interest could chose for the study.
When are two variables said to be confounded?
When their effects on the response variable cannot be distinguished from each other.
In 2015, a BYU professor investigated the impact that social isolation has on early mortality. This professor discovered that individuals that experienced social isolation had a higher likelihood of mortality than individuals that did not experience social isolation. (Source: Holt-Lunstad, Julianne et al, "Loneliness and Social Isolation as Risk Factors for Mortality: A Meta-Analytic Review", Association for Psychological Science, April 2015.) What is the explanatory variable in this scenario? What is the response variable in this scenario?
Whether an individual experienced social isolation The likelihood of mortality experienced by individuals
An experiment was designed using school children as subjects to determine whether milk prevented their catching colds. The researcher randomly assigned 100 school children to two groups - one group of 50 to receive a cup of milk at school each day and the other group of 50 to receive no milk at school. What is the response variable? Remember: The response variable is measured on the individual. what is the explanatory variable?
Whether the child caught a cold A response variable is a variable that gives the result (may not be a number) of the outcome of a study; measured on an individual. In this case we were measuring if the individual caught a cold or not. Whether the child received a cup of milk at school each day The explanatory variable is a phrase that describes all possible treatments, in this case the two treatments were the child receiving milk or the child not receiving milk.
An experiment was designed using school children as subjects to determine whether drinking milk prevented their catching colds. The researcher randomly assigned 100 school children to the two groups - one group of 50 to receive a cup of milk at school each day and the other group of 50 to receive no milk at school. What is a potential lurking variable?
Whether the child was frail or robust at the beginning of the experiment If a child is already more frail when the experiment begins they will be more likely than a robust child to catch a cold. The other answers are incorrect because at the start of the experiment we assign the children to milk or no milk, the response is if the child caught a cold, and if they are a poor student verses a good student will not affect their health.
How quickly should you expect a response after you email the Course Assistants?
Within two school days.
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. Referring to the question above, was replication incorporated? What type of study is this?
Yes, because each treatment group had 20 subjects A matched pairs experiment.
An experiment was designed using school children to determine whether drinking milk prevented their catching colds. The researcher randomly assigned 100 school children to two groups—one group of 50 to receive a cup of milk at school each day and the other group of 50 to receive no milk at school. Does the study incorporate control/comparison? Does the study incorporate replication?
Yes, because the "No milk" group was compared to the "Received milk" group. A control is an inactive treatment where no experimental condition is applied to the individuals in order to determine whether the active treatment works. We can also have a comparison when there at least two treatments administered. Yes, since there were 50 children in each treatment group. Replication is when there is more than one subject in EACH treatment group.
What should you use as your student ID when you register your iClicker?
Your myBYU NetID login. In the iClicker quizzes section of the syllabus it says "You must register with your NetID, NOT your 9-digit BYU ID number."
Why do we sample?
census is too expensive. A census is time consuming. A census may be impractical. The point of taking a sample is because we can not get all of the data we want from a population. There are multiple reasons for this: costs, time, and practicality.
For exam and credit quiz issues, who should you contact?
email [email protected] If you have any questions or concerns regarding the exams or quizzes, please send an email to [email protected] as soon as possible. All questions should be directed to the exam/homework CA rather than your TA, your professor, or the course manager. If you need to contact your professor, the CAs, or your TA, please use the appropriate email addresses found in the syllabus and never use the Learning Suite messaging system.
The group we want to study or learn something about is known as the
population. All statistics is about making inferences about our population. We do this by taking a sample of individuals or groups to estimate what the population is like.
