CH. 1 Homework

(1) Additional variables that can influence the outcome of a study/experiment are called lurking variables. To ensure that these unforeseen influences are removed, a researcher can use random assignment to fill the control and treatment groups. (2) To eliminate "the power of suggestion", a researcher can perform a blind or double-blind study/experiment. Which statements are true

Both 1 and 2

The school district randomly selects 3 high schools in the district and then collects data on PSAT score for all 9th graders in those districts

Cluster sample

Topic study: does owning a dog help a heart heal faster?

Confounding variable: The exercise an owner got while walking his/her dog Can confounding variables prevent a researcher from determining cause and effect? Yes

What is important in statistical thinking?

Controlling for sampling or non-sampling error. Designing a study that will be replicable

The school district collects data on the PSAT score of the first 50 scores that are entered in to the system

Convenience sample

In a study of a weight loss program, 23 subjects lost an average of 14 lbs after 7 weeks. Methods of statistics can be used to show that it is unlikely to get these results by chance if the diet had no​ effect.

Does the weight loss program have statistical significance? Yes Does the weight loss program have practical significance? Yes

Number of pills taken each day: Determine whether the variable given is qualitative, quantitative-discrete, or quantitative-continuous

Quantitative- discrete since this variable would yield numbers

Thickness of an aluminum can: Determine whether the variable given is qualitative, quantitative-discrete, or quantitative-continuous.

Quantitative-continuous since the variable would yield numbers that measure

A restaurant wants to estimate the percentage of customers who pay cash. They look at a sample of 50 customer receipts from the week.

Sample: 50 customer receipts Population: all customer receipts Parameter: the percentage of all customer receipts that were paid for with cash Individual: a customer receipt Statistic: the percentage of 50 customer receipts that were paid for with cash Variable: whether or not it was paid for with cash

In a study, the sample is chosen by pulling 50 names from a hat

Simple Random

A school district has a list of all of its 9th grade students. They then collect data on the PSAT score of 30 randomly selected students

Simple random sample

For the scenario, determine if the survey is a random survey or a biased survey. Explain your reasoning. 5. A local bookstore offered all of their customers a $10 gift certificate to complete a brief online survey in order to determine the most popular reading genre.

Biased Survey, Prize was offered

What is a lurking variable?

A lurking variable is a variable that causes both the explanatory and response variable to change during the study.

Should our state spend more money on colleges and less on roads? Is the question biased?

No

If there is a positive correlation between the number of liquor stores in a neighborhood and the amount of crime, can we conclude that closing liquor stores will reduce the amount of crime?

No, because correlation does not mean causation

Determine whether each correlation implies causation. Days of high umbrella sales see higher incidences of traffic accidents.

No, just because there is evidence of a correlation between variables, this does not mean that changing one will cause a change in the other.

A researcher wants to determine if a new drug lowers the blood pressure of patients with high blood pressure. The patients are randomly selected to be in the study and they pick which group to be in. Is this randomized experiment? Why or why not

No, since the treatment is not randomly selected by the researcher

A doctor wants to know if treatment A or treatment B works faster on removing a wart. He randomly selects a sample of people who had gotten treatment A and a sample of people who have gotten treatment B Is this observational or experiment

Observational study

A researcher wants to evaluate whether countries with lower fertility rates have a higher life expectancy. They collect the fertility rates and the life expectancies of countries around the world. Is this observational or experiment

Observational study

Student ID number: Determine whether the variable given is qualitative, quantitative-discrete, or quantitative-continuous.

Qualitative since this variable would yield categories

An online instructor wants to estimate the mean amount of time that students spend in the online homework system on a particular homework assignment. The instructor takes a random sample of 30 students and looks up the amount of time recorded by the system for that assignment.

Statistic: mean time spent on a particular homework assignment for 30 students in that instructors online class Population: all students in that instructors online class Individual: a student in that instructors online class Sample: 30 students in that instructors online class Variable: time spent on a particular homework assignment Parameter: mean time spent on a particular homework assignment for all students in that instructors online class

The school district divides the 9th grade students by high school attended and then collects data from a random sample of 9th grader from each high school

Stratified random sample

The school district has a list of all 9th grade students and then collects data on the PSAT score of every 10th student on the list

Systematic sample

The science club at a large middle school has 25 members. The members want to survey a sample of 125 students to estimate the percentage of all students at the school who plan to submit a science-fair project. Each member of the club asks 5 friends the following question: "Will you be submitting a project to the science fair this year?" Of all the friends, 76 percent replied with a "yes." Which of the following is a reason why the sample selection method described is NOT fair?

The club members only surveyed their friends, so the sample is not likely to be representative of the students at the school. Friends tend to share the same views as each other, the sample would be bias

Over a period of a few years, the population of Boston increased. It was observed that during this period the correlation between the number of people attending church and the number of people receiving traffic tickets was r = 0.92 (a very high measure of linear correlation). Does going to church cause people to get traffic tickets? Is there a lurking variable that might cause both variables to increase?

The increase in population is a lurking variable that caused both variables to increase

What is the definition of statistics

The study of how to collect, organize, analyze, and interpret data collected from a group.

Over the years it has been said that coffee is bad for you. When looking at the studies that have shown that coffee is linked to poor health, you will see that people who tend to drink coffee don't sleep much, tend to smoke, don't eat healthy, and tend to not exercise. Can you say that the coffee is the reason for the poor health or is there a lurking variable that is the actual cause?

There is a lurking variable that is the actual cause

Given humanity's great tradition of exploration, do you favor continued funding for space flights? Is the question biased?

Yes

To determine if lack of exercise reduces flexibility in the knee joint, physical therapists ask for volunteers to join their trials. They then randomly select the volunteers to be in the group that exercises and to be in the group that doesn't exercise. Is this a randomized experiment? Why or why not?

Yes, since the treatment is randomly selected by the researcher

A doctor gives some of the patients a new drug for treating acne and the rest of the patients receive the old drug. The doctor randomly chooses a medicine for each patient. The patient does not know which treatment they are getting. Is this a blind experiment, double blind experiment, or neither? Why?

blind, since the researcher knows who is getting which treatment but the individual does not

To see how well a weight loss drug works, a doctor randomly selects which people in the study will be given the actual drug and which will be given a placebo. All study participants think they are getting the weight loss drug. Is this a blind experiment, double blind experiment, or neither? Why?

blind, since the researcher knows who is getting which treatment but the individual does not