stat

STAT 350 (Spring 2017) Homework 6 (20 points + 1 point BONUS 1

In this problem set ONLY, you do not need to explain your answer unless requested. Practice Problems: 1.21 (p. 22), 1.23 (p.22) (2.5 pts.) 1. Oregon Scientific has come under suspicion of purposely shipping defective

wireless weather stations. The Attorney General’s office in Delaware would like to estimate the proportion of defective products being shipped by this company. Out of the 50 closest TV stations that were contacted by the office, 30 had received wireless weather stations from Oregon Scientific. The Attorney General's office asked each of these 30 stations if the weather stations were defective.

(1 pt.) a) Is this an observational or an experimental study? Please explain your answer. (0.5 pts.) b) Describe the sample in this problem. (1 pt.) c) Is this a SRS? Justify your answer. If this is not a SRS, how would you change the

sampling technique so that it would be random. (3.5 pts.) 2. The ceramic tile used to construct the floors in a mall must be sturdy, easy to clean,

and long-lasting. Before determining which tiles to use, a construction firm orders 25-tile boxes from five different manufacturers (five boxes from each of the five manufacturers) and uses a standard strength test on each tile.

(1 pt.) a) Is this an observational or an experimental study? Please explain your answer. (0.5 pts.) b) What is the unit or population in this study? (0.5 pts.) c) What is the factor or treatment in this study? (0.5 pts.) d) What is the outcome variable of this study? (1 pt.) e) State a possible source of bias in this study. Feel free to speculate beyond the explicit

statement of the question. However, nothing that is assumed can be in contradiction to what is stated. Please include any assumptions that you are making.

(2 pts. + 1 pt. BONUS) 3. As the weather is so warm this year, more and more students are

exercising outside instead of in the rec center. A researcher wanted to know which type of activity – walking, running, or ultimate Frisbee – was more rewarding to the students. Therefore, she randomly assigned 90 college students to each of the three activities. After one month, the researcher asked each of the participants if they enjoyed the assigned activity.

(1 pt.) a) Draw the correct experimental design of this study. (1 pt.) b) Describe a possible methodology that could be used to decide which students will be

assigned to which activity. (1 pt. BONUS) c) Is this study well-designed? If not, how would you change the design method.

Please explain your answer. (1 pt.) 4. A marketer wants to know whether men and women respond differently to two different

ads. Draw the correct experimental design to take this into account. Hint: In the design, it is better to start off with the ads. Remember to clearly indicate what is randomized.

STAT 350 (Spring 2017) Homework 6 (20 points + 1 point BONUS 2

(1 pt.) 5. Researchers wants to determine if climbing stairs is more effective at loosing weight than walking. Consider the following observational study and experiment:

Observational study One researcher finds 100 overweight, but not obese, men in their 30's who regularly climb at

least 10 flights of stairs a day. In addition, she finds 100 overweight, but not obese men in their 30's who regularly walk 1 mile a day. The researcher takes their weight at the beginning of the study and then two months later.

Experiment Another researcher finds 200 overweight, but not obese men in their 30's. She randomly

assigns 100 of the men to climb 10 flights of stairs a day. The other 100 men are assigned to walk 1 mile a day. The researcher takes their weight at the beginning of the study and then two months later.

Which of the two, the given observational study or the given experiment, gives better

information about the relationship between these variables? Please explain your answer. (1 pt.) 6. As Valentine's Day approaches, a candy store wanted to know which type of chocolate

was preferred by their customers, either milk chocolate or dark chocolate. The store debated which of two possible experiments they would use. In experiment 1, each customer evaluates both types of chocolates. In experiment 2, each customers rates one type of chocolate.

Experiment 1 Flip a coin for each customer to choose which types (s)he will taste first. Ask which of the two

types of chocolate that (s)he prefers. Experiment 2 Flip a coin for each customer to choose which type (s)he will taste. Then each person rates the

chocolate from 1 to 10. Which of the two given designs can be considered as the better design? Please explain your

answer. (2 pts.) 7. Please indicate what type of sampling design is most appropriate for each of the

following studies. The choices are SRS, stratified random sampling, and matched pair design.

(0.5 pts.) a) A student organization has 55 members. Out of these members, five are selected

randomly to attend a conference. (0.5 pts.) b) The course coordinator of an introductory statistics class randomly selects students

who are taking the online section and students who are taking traditional face-to-face sections and measures their performance on the first midterm.

(0.5 pts.) c) Does a cancer treatment have dangerous side effects? 50 female mice are given the treatment and 50 female mice were treated identically except that they did not receive the treatment.

(0.5 pts.) d) A study to compare two methods of painting wood started with boards of oak. Each board was ripped from end to end to form two edge-matched specimens. One was assigned to Method A; the other to Method B

STAT 350 (Spring 2017) Homework 6 (20 points + 1 point BONUS 3

Additional Problems: 1.27, 1.29, 1.31, 1.35, 1.37, 1.39 (2.5 pts.) 8. A certain high school records whether the students eat breakfast or not to

determine if they should start a free hot breakfast program. A study shows that high school students who don't eat breakfast have a lower grade average than students who do eat breakfast. From this study, the school administration suggest that they should start a free hot breakfast program. Another possible explanation is that students who don't eat breakfast are poorer than the students who do eat breakfast at home and the economic situation of their parents is causing the lower grades, not the lack of breakfast.

(0.5 pts.) a) What is the explanatory variable in this study? (0.5 pts.) b) What is the response variable in this study? (0.5 pts.) c) What is the lurking variable in this study? (1 pt.) d) Draw a diagram that explains your choice. (Possible diagrams are causation, common

response or confounding). (2 pts.) 9. Children who watch many hours of television tend to get lower grades in school, on

average, than those who watch less TV. Does this mean that watching more TV lowers grades in school?

(1 pt.) a) What is a possible lurking variable in this study? (1 pt.) b) Draw a diagram that explains your choice. (Possible diagrams are causation, common

response or confounding). (2.5 pts.) 10. Students enrolling in an elementary statistics course take a pretest that assess

their math skills. Those who receive low scores are given the opportunity to take three one- hour refresher sessions designed to review the basic math skills needed for the statistics course. Those who took the refresher sessions performed worse than those who did not on the final exam in the statistics course.

(0.5 pts.) a) Is the following statement true or false: Does this mean that the refresher course

has a negative impact on performance? (1 pt.) b) What is a possible lurking variable in this situation? (1 pt.) c) Draw a diagram that explains your choice. (Possible diagrams are causation, common

response or confounding).