STAT MIDTERM! - Carmen Homework!
Suppose the correlation between X and Y is .3. If you double all the X values and double all the Y values, the correlation between 2X and 2Y is .6.
False
The second level branches on a tree are marginal probabilities.
False
There can be different amounts of data in each section of a boxplot.
False
True or False: The best fitting line always has an SSE of 0.
False
Which of the following statistics can NEVER be negative?
a. Correlation b. Slope of the regression line c. Y-intercept of the regression lined. d. All of the above can be negative, if the data permits. All of the above can be negative, if the data permits. !!!!
. Bob collected data to compare years of education and hours watching TV in the last month, to see if a relationship exists. His computer output is shown below. Based on this information, is there a strong linear relationship? Predictor Coef Constant 8.290 Education -3.1460
a. Yes b. No c. Can't tell with the information given Can't tell with the information given !!!!!!
Which type of probabilities are in each of the 4 cells of a two-way table of probabilities?
"And" probabilities
Suppose you are using cereal price to predict milk price; they have a correlation of -.70. The average cereal price is $3.00 with standard deviation $0.50 and the average milk price (gallon) is $2.50 with standard deviation $0.25. What is the slope of the regression line? Choose the closest answer.
-.35
A business has 3 branches, A, B, and C. Branch A gets 20% of the business, Branch B gets 50%, and Branch C gets 30%. We know the following information: Branch A: chance of running out of single dollars in a day is .15 Branch B: chance of running out of single dollars in a day is .05 Branch C: chance of running out of single dollars in a day is .10. What is the chance that you go to Branch A and they will have run out of single dollars? Choose the closest answer
.03
If P(A) = .2, P(B) = .3, and P(A|B) = .1, what is P(A and B)?
.03
P(A) = .3, P(B|A) = .4, P(B) = .5 What is P(A and B)?
.12
The probability that a person will buy something when a telemarketer calls is .10. A telemarketer calls two people at random. What is the probability of getting at least one person to buy something?
.19
What is the standard deviation of the data set 1, 1, 1, 1?
0
Undercoverage means you had alot of nonresponse in your sample.
False
Undercoverage occurs when a certain group from the population is sampled but does not respond.
False
Suppose the correlation between speed (mph) and gas mileage (mpg) is -.65 and the slope of the regression line is -.123. That means if you increase your speed by 10 mph, what will happen to your gas mileage?
It will decrease by 1.23 mpg
Which five descriptive statistics do you need to find the equation of the best fitting line?
Mean of X, Mean of Y, SD of X, SD of Y, and r.
A correlation of -.6 is considered to be what?
Moderately Strong
Two buses (Bus A and Bus B) take all the children home from their school. Bus A takes 40% of the children; Bus B takes 60% of the children. Of those who ride Bus A, 20% are in kindergarten. Of those who ride Bus B, 10% are in kindergarten. Suppose a bus rider is in kindergarten. Are they more likely to ride Bus A or Bus B?
More likely to ride bus A.
5% of people read the paper every day. 30% of women read it, and 20% of men read it. Are gender and reading the paper independent?
No
The equation of a regression line is Y = 20 + 5X where X = hours studied and Y = exam score. Study time data ranged from 8 to 15 hours. Should we interpret the Y-intercept here?
No. You should not interpret the Y-intercept in this situation.
Suppose 40% of the new employees at your company are males and 30% of the "old employees" are males. What percentage of ALL the employees are male?
Not enough information to tell
If you are predicting U.S. movie box office revenue by using Opening Weekend Revenue, which variable is X and which is Y?
Opening Weekend Revenue is X and U.S. Box office revenue is Y.
Extrapolation is what?
Plugging in X values outside the range of the data
Which of the following is NOT a property of standard deviation?
Standard deviation is never negative. b. Standard deviation has no units. c. Standard deviation is affected by outliers and skewness. d. All of the above are properties of standard deviation. Standard deviation has no units. !!!!!
When a difference in treatment is decided to be due to more than random chance, what do you call the results?
Statistically significant
The correlation between study time for an exam (in minutes) and exam score is 0.79. If we convert study time to hours, the correlation will
Stay the same
If you add 10 to every value of a data set, what happens to the standard deviation?
Stays the same
If you want to ask the question: "How is the view from your seat?" where your population is the OSU's football stadium, what kind of sample should you use?
Stratified Random Sample
The results of a well-designed experiment are ____________ than the results of a well-designed observational study (assuming it is ethical to do an experiment.)
Stronger
If you are predicting gas price using temperature, which is the X variable?
Temperature
Which measure of variability measures the concentration of the data around the mean?
The Standard Deviation
SSE is equal to what?
The Sum of Squares for Error for any line going through the data.
A boxplot is a one-dimensional graph
True
f the median is closer to Q1 than it is to Q3 then the data is skewed right.
True
response bias?
answers incorrectly
An experiment gives 3 different dosage levels of a drug to 3 groups of people. The first dosage level is a fake pill (or placebo) for comparison. We measure the blood pressure of the participants before and after the study and write down the amount by which blood pressure changed. What is the response variable?
blood pressure change
A listing of all possible values in a data set and how often they occurred is called a data _____________________.
distribution
A five number summary contains the min, max, Q1, Q3, and what other value?
the median, Q2, or 50th percentile
If the correlation is zero, what is the equation of the best-fitting regression line through the data?
y=y bar (line above thing)
If you could choose four numbers from 1, 2, 3, 4 and repeated numbers were allowed (such as 1, 1, 3, 2), which set of four numbers would give you the largest standard deviation? (No calculations needed.)
1,1,4,4
Suppose 35% of OSU students own an iPad, 25% own a laptop, and 10% own both. What percentage of OSU students own at least one of those items?
50%
What kind of sample occurs when you put an ad in the newspaper and ask readers to take your survey?
A self-selected sample
If you switch X and Y, which of the following will change?
Both b and c will change
Which is best if you want to compare several data sets regarding shape, center, and variability?
Boxplot
A flat histogram (with a line straight across) contains no variability whatsoever, according to our definition.
False
If you add the same value to every single number in a data set, the standard deviation also changes by that same value.
False
Standard deviation has no units.
False
The 4 cells of a two way table contain conditional probabilities.
False
What are the units of the residuals?
Same as the units of Y
When finding the correlation if you are given R-squared, you take the square root first. Then what do you look at to determine the sign for the correlation?
The sign on the slope
How to the residuals relate to the SSE?
The sum of the squared residuals equals SSE.
The median is not affected by outliers
True
The wording of a survey question can affect the results: True or False?
True
True or false: You cannot see the mean on a boxplot.
True
You can have two data sets with the same mean but different standard deviations.
True
Confidentiality is ________________ than anonymity.
Weaker
Bob runs an experiment to see which brand of paper towel is more absorbent: Brand A or Brand B. He takes a random sample of 10 sheets from each brand of paper towel and puts each sheet in a cup of water and measures how much water was absorbed by the sheet by squeezing it tightly for 10 seconds and weighing the water that comes out. What is the response variable?
Weight of the water squeezed out
The third quartile is the same thing as the _____________ percentile
75th
All good samples are _____________.
Random
When an individual in the sample responds but does not give the correct data, this is called:
Response Bias
You send out an email to all the students in Stat 1430 and you tell them to go to your website and do a survey. 100 students come forward. What kind of sample is this?
Self-selected sample
To find the best fitting line, you find the line with the ________ SSE.
Smallest
A listing of all the possible values of a data set and how often they occur is called a distribution.
True
A longer box in the boxplot means more variability in the data.
True
If you multiply every single number in a data set by the same value, the standard deviation is also multiplied by that same value.
True
The slices on a pie chart represent relative frequencies.
True
The starting point can affect the way a graph looks.
True
You randomly choose 100 students from Stat 1350 to take a survey. 60 of them take the survey. What can occur with the other 40 people?
nonresponse bias
Mike marks down the gas mileage of his two cars every time he fills them up with gas for 6 months straight. At the end he notes that his Mustang gets better mileage than his Corvette. Is this an experiment or an observational study?
observational study
The five-number summary of a single data set of 100 numbers would be which of the following?
the 5 numbers that are marked off on a boxplot
As we heard in lecture, the "average distance from the mean" is measured by the __________________________.
Standard Deviation
A business has 3 branches, A, B, and C. Branch A gets 20% of the business, Branch B gets 50%, and Branch C gets 30%. We know the following information: Branch A: chance of running out of single dollars in a day is .15 Branch B: chance of running out of single dollars in a day is .05 Branch C: chance of running out of single dollars in a day is .10. What is the chance that you go to any branch of this business and they will have run out of single dollars? Choose the closest answer
.10
P(A) = .2 and P(B) = .3. Suppose A and B are independent. What is P(A or B)?Choose the closest answer.
.40
If r = -.7, what is the value of the coefficient of determination?
.49
P(A) = .2 and P(B) = .3. Suppose A and B are disjoint. What is P(A or B)?Choose the closest answer.
.50
A business has 3 branches, A, B, and C. Branch A gets 20% of the business, Branch B gets 50%, and Branch C gets 30%. We know the following information: Branch A: chance of running out of single dollars in a day is .15 Branch B: chance of running out of single dollars in a day is .05 Branch C: chance of running out of single dollars in a day is .10 Which Branch is most likely to run out of single dollars in a day?
A
Bob wants to estimate the percentage of people who own a dog in his town, and he goes to all the apartment buildings to carry out his survey. He leaves out all the houses in the town. What kind of bias is this?
Bias due to undercoverage
Which type of graph of quantitative data fits the following description: It shows skewed vs. symmetric shapes; it's easy to determine center and variability; it's good for skewed data sets; and it's easy to compare data sets:
Boxplot
Bob runs an experiment to see which brand of paper towel is more absorbent: Brand A or Brand B. He takes a random sample of 10 sheets from each brand of paper towel and puts each sheet in a cup of water and measures how much water was absorbed by the sheet by squeezing it tightly for 10 seconds and weighing the water that comes out. What is the independent variable?
Brand of paper towel (A or B)
What is the statistical definition of a random sample? Choose the best answer.
Every sample of that same size has an equal chance of being selected.
If there is no relationship between two variables in a two-way table, then the two variables are said to be:
Independent
Which of the following is NOT a property of correlation?
It has no units. b. Switching X and Y does not change its value c. It is not affected by outliers and skewness. d. All of the above are properties of correlation. It is not affected by outliers and skewness. !!!!!
uppose 40% of the new employees at your company are males and 60% of the "old employees" are males. Are gender and type of employee (new/old) independent?
No
In our lecture notes is an example involving two hospitals, A and B. If you compare patient outcomes for the hospitals, B is safer (has a lower death rate). But if you look only at the patients in poor condition, A is safer, and if you only look at the patients in good condition, A is safer. What is going on with this example?
Simpson's Paradox
What is the most common observational study?
Survey
Which can affect the way a histogram looks?
The number of bars used, The scale on the Y axis, The starting point on the Y axis - ALL OF THE ABOVE!
A confounding variable can cause the results of a two-way table to reverse when it is added to the data set.
True
P(A) = .20, P(B) = .30, P(A and B) = .06. Are A and B independent?
Yes
What is statistical significance?
a result due to more than a chance
Suppose the best fitting line is Y = 3+ 20X, where X is hours studied and Y is exam score. How do you interpret the slope of the line?
a. As hours studied increases by 3, exam score increases by 20. b. As exam score increases by 1, hours studied increases by 20. c. As hours studied increases by 1, exam score increases by 3. d. None of the above. None of the above !!!!!
Which of the following is NOT in the same units as the original data?
a. standard deviation b. Q1 c. y-intercept of the regression lined. All of the above are in the same units as the original data. All of the above are in the same units as the original data. !!!!!!!!
Your company operates in 4 regions and your boss numbers them 1, 2, 3 4. Is this variable quantitative or categorical?
categorical
Which is better to use to see the most clear pattern in the data?
histogram
Suppose X and Y have a correlation of .9 and the regression line is Y = 2X + 3. If you increase X by 5 what happens to Y?
increase by 10
Which of the following is the X variable in an experiment?
independent variable, or factor
If the correlation is .2 what does that tell you about using a regression line to fit your data?
it's a weak positive linear relationship, do not proceed with a regression line
A business has 3 branches, A, B, and C. Branch A gets 20% of the business, Branch B gets 50%, and Branch C gets 30%. We know the following information: Branch A: chance of running out of single dollars in a day is .15 Branch B: chance of running out of single dollars in a day is .05 Branch C: chance of running out of single dollars in a day is .1 Suppose a Branch has run out of single dollars and you get the phone call. Is it most likely to be Branch A, Branch B, or Branch C?
A or C
If the mean of a data set is large, the standard deviation has to be large also.
False
The median must be one of the numbers in the data set
False
IQR is affected by outliers.
False
If the correlation is 0 you know there is no relationship between X and Y.
False
If there are a few very small values in a data set compared to the rest of the data, the mean will be larger than the median.
False
Correlation is in the same units as X and Y.
False
Suppose the probability of having a female in your stat class is .6, and of the females in your stat class, 30% are accounting majors. Of the males in your class, 40% are accounting majors. What percentage of all students in your stat class are accounting majors?
34%
Correlation measures the strength and direction of any relationship between X and Y.
False
What does it mean for a sample to be truly random, according to our notes?
Every sample of the same size has the same chance of being selected.
A confidential survey is one in which they cannot link you to your data.
False
A flat histogram indicates no variability in the data.
False
Bob picks a name from the phone book using a random number generator, and then takes the first 100 names that come after that to make a sample. Is Bob's sample random?
False