Stat Final: Unit 4
A random sample is...
A sample that gives every possible sample of the same size the same chance to be selected
Which of the following is the best description of a simple random sample of size n from a population of size N
A sampling method in which every group of individuals of size n is equally likely to be selected
we wish to choose a simple random sample of size three from the following list of employees of a small company. To do this, we will use the numerical labels attached to the names below. The sample you obtain is...
Bechhofer, Tylor, and Weiss
Mrs. Singleton will be measuring the total amount of leaf litter in a random sample (n=5) of forest sites selected without replacement from a population of 45 sites. The sites are labeled 01,02,...., 45 and she starts at the beginning of the line of random digits and takes consecutive pairs of digits. Which of the following is correct.
Her sample is 38, 35, 02, 22, 40
What is the principal purpose of control in a randomized comparative experiment?
Isolating the effect of the treatment variable by keeping all other variables the same in the treatment groups
Below is a dot plot of the percentage of made free throws by a 60% free-throw shooter in 100 computer simulations of 16 free throws.....Brayden was a 60% free throw shooter last season. He practiced all through the off-season and had made 12 of the first 16 free throws this season. Based on his performance and the results of the simulation, is there convincing evidence that Brayden has improved his free-throw percentage? Explain.
No. The simulation shows that there is a 14% chance of doing that well or better even if he is still a 60% free throw shooter.
Some studies of the relationship between car color and frequency of accidents have found that red cars are more likely to be in accidents than black cars, despite how visible they are. Some experts warn that we should not conclude that red cars are less safe than black cars, because of possible confounding. Which of the following best describes what this means?
Studies of this type are all observational, and it is not possible to separate the effect of car color form the type of people who choose to drive red cars.
An article in the student newspaper of a large university had the headline "A's swapped for evaluations?" The article included the following .... Results showed that higher grades were associated with better evaluations. Which of the following would be a valid conclusion to draw from the study?
Teachers of courses in which the mean grade is above average tend to have above-average teaching evaluations.
An Atlanta school district wants to compare the effectiveness of a standard AP Statistics curriculum and a new "hands-on" AP Statistics curriculum. Two experienced teachers, Mrs. Davis and Mr. Cohen each teach one class with the standard curriculum and one with the new approach. Students are assigned at random to these four classes. At the end of the year, all students take the AP Statistics exam. Which of the following are experimental units in this experiment?
The students in the four classes
A political action committee send out a questionnaire to randomly-selected mailing addresses, asking people to rate the importance of a variety of economic and social issues facing the country. At the end of the questionnaire is an (optional) invitation to donate money to the political actions committee. Which of the following statements about this survey is true?
The survey results will overestimate support for this political action committee in the entire population because people are more likely to respond if they are prepared to donate money
For the track coach's study described in the previous exercise, which of the following best describes a conclusion that can be drawn?
We can determine whether the new training program improves race times more than the standard program for distance runners like those in this study
A track coach wants to test the effectiveness of a new training program for distance runners. He selects his two fastest runners and, using a coin flip, randomly chooses one to participate in the new program. The other will continue with the standard training regimen. He then picks the next two fastest runners and randomly signs each one to a program. He repeats this process with all his runners, choosing the two fastest remaining each time. he then compares race times within each group of two runners. This study uses which of the following?
a matched pairs design
Mr. Miller wants to study the effect of storage time (6, 12, and 18 months) on the amount of vitamin C present in freeze dried fruit when stored for these lengths of time. Six fruit packs were randomly assigned to each of the three storage times. The treatment, experimental unit, and response are respectively...
a specific storage time, a fruit pack, amount of vitamin C
Mrs. De La Fe, a sportswriter, wants to know how strongly Orland residents support the professional baseball team, the Orlando Rays. She stand outside the stadium before a game and interviews the first 20 people who enter the stadium. The intended population for this survey is....
all residents of orlando
A marine biologist wants to estimate the mean size of a barnacle Semibalanus balnoides on a stretch of rocky shoreline. To do so he randomly selected twenty 10 by 10 square inch plots and measured the size of every barnicle in each plot. This is an example of...
cluster sampling
The reason that blocking (as in randomized block design) is sometimes used in experimentation is to...
compensate for anticipated differences in the response variable for different values of a specific "blocking" variable.
If changes in a response variable are due to the effects of the explanatory variable as well as the effects of another variable, and we cannot distinguish between these effects, we are said to have...
confounding
The Texas experiment described in the previous question...
has two factors: the type of AP Statistics curriculum and the teacher a student is assigned to
We say that the design of a study is biased if...
it is very likely to underestimate or very likely to overestimate the value you want to know
One hundred volunteers who suffer from severe depression are available for a study. Fifty are selected at random and are given a new drug that is thought to be particularly effective in treating severe depression. The other fifty are given an existing drug for treating severe depression. A psychiatrist evaluates the symptoms of all volunteers after four weeks in order to determine if there has been substantial improvement in the severity of the depression. The study would be double blind if...
neither the volunteers nor the psychiatrist knew which treatment and person had received.
Frequently, telephone poll-takers call near dinner time (between 6 pm and 7 pm) because most people are at home then. This is an effort to avoid...
nonresponse
A civil engineer is testing the reliability of traffic signal controllers produced by two different companies. He has 20 sets of controllers from each company, and he has been given clearance to install them at 40 different intersections in the city. He randomly assigns the controllers from company A to 20 intersections and the controllers from company B to the other intersections. The most important reason for this random assignment is that...
randomization is a good way to create two groups of 20 intersections that are as similar as possible, so that comparisons can be made between the two groups.
A public opinion poll in Ohio wants to determine if registered voters in the state approve a measure to ban smoking in public areas. They select a simple random sample of fifty registered voters from each county in the state and ask whether they approve or disapprove the measure. This is an example of a...
stratified random simple
A sportswriter wants to know how strongly Lafayette residents support the local minor league baseball team, the Lafayette Leopards. She stands outside the stadium before a game and interviews the first 20 people who enter the stadium. The newspaper asks you to comment on their survey method. You say...
this is a convenience sample. It will most certainly overestimate the level of support among all Lafayette residents
A market research company wishes to find out whether the population of students at a university prefers brand A or brand B of instant coffee. A random sample of students is selected, and each one is asked to try brand A first then brand B (or vice versa, with the order determined at random). They then indicate which brand they prefer. The response variable is...
which brand they perfer