practice midterm test answers 1
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 correlation of -.6 is considered to be what?
Moderately strong
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
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
Which is best if you want to compare several data sets regarding shape, center, and variability?
box plot
Your company operates in 4 regions and your boss numbers them 1, 2, 3 4. Is this variable quantitative or categorical?
categorical
The 4 cells of a two way table contain conditional probabilities.
false
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
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
Suppose 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
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
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
A boxplot is a one-dimensional graph
true
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
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
Correlation is in the same units as X and Y.
false
Correlation measures the strength and direction of any relationship between X and Y.
false
Standard deviation has no units.
false
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
Undercoverage means you had alot of nonresponse in your sample.
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
If the median is closer to Q1 than it is to Q3 then the data is skewed right.
true
The median is not affected by outliers
true
P(A) = .20, P(B) = .30, P(A and B) = .06. Are A and B independent?
yes
P(A) = .3, P(B|A) = .4, P(B) = .5 What is P(A and B)?
.12
P(A) = .2 and P(B) = .3. Suppose A and B are independent. What is P(A or B)?Choose the closest answer.
.40
P(A) = .2 and P(B) = .3. Suppose A and B are disjoint. What is P(A or B)?Choose the closest answer.
.50
The third quartile is the same thing as the _____________ percentile
75th
What is statistical significance?
A result due to more than chance
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.
Extrapolation is what?
Plugging in X values outside the range of the data
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
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
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
