Hw 1 chapter 6 stats 231

Which choice best describes a simple random sample?

Answer: a selection of members from a population in such a way that every possible sample of the same size has an equal chance of being chosen

The Centers for Disease Control and Prevention conduct the yearly National Health Interview Survey (NHIS). A description of their methodology is given: "To achieve sampling efficiency and to keep survey operations manageable, cost‑effective, and timely, the NHIS survey planners used multistage sampling techniques to select the sample of persons and households for the NHIS. These multistage methods partition the target universe into several nested levels of strata and clusters. The NHIS target universe is defined as all dwelling units in the U.S. that contain members of the civilian non‑institutionalized population." (a) What is the population of interest? Select the correct answer.

(a)

The National Halothane Study was a major investigation of the safety of anesthetics used in surgery. Records of more than 850,000h anesthetic operations performed in 34 major hospitals showed death rates for four common anesthetics: Anesthetic A B C D Death rate 1.7% 1.7% 3.4% 1.9% There is a clear association between the anesthetic used and the death rate of patients. Anesthetic C appears dangerous. (a) Select the best explanation for why we call the National Halothane Study an observational study rather than an experiment, even though it compared the results of using different anesthetics in actual surgery. (b) when the study looked at other variables that are cofounded with a doctors choice of anesthetic, it found that anesthetic C was not causing extra deaths. Suggest the important lurking variables that are founded with anesthetic a patient receives.

(a) In order to be an experiment, the treatments (choice of anesthetic) would have to be randomly assigned. Instead, a patient's anesthetic is selected by his or her doctor(s). (b) We should consider the type of surgery and the age, sex, and condition of the patient. These factors may determine the type of anesthetic given to the patient.

A study examined a large nationally representative sample of American adults age 18 to 64 years. The primary outcome of interest was body mass index (BMI), which was also used to categorize participants as obese (BMI≥30) or not obese (BMI<30) . In the study, inadequate hydration (as evidenced by a urine osmolality ≥800 mOsm/kg) was associated with higher BMI and obesity. The published findings include this statement: "Although inadequate intake of water among obese adults may explain the observed findings, differential consumption of food with high water content may also contribute to the relationship between inadequate hydration and elevated BMI."

(a) Is this study observational or experimental?This is Answer: an observational study. (b)What variables recorded for each participant are described in the study? Answer: BMI and urine osmolity (c) What given lurking variable is confounded with the explanatory variable? Answer:Consumption of food with high water content is offered as a possible confounding variable. (d)

Classify each description as either an observational study or an experiment. 1. In a sleep study designed to test whether a new supplement helps individuals sleep longer, a computer randomly assigns each participant either to a group receiving the supplement or to a group receiving an inactive pill. 2. A political scientist seeks to determine if women between the ages of 25 and 30 are more likely than men of the same age to vote for a Democratic candidate. The scientist selects a sample of voters from this age group to survey their political preference. 3. Agricultural scientists seek to test the effects of a new pesticide on corn crops. Half of the participating farmers are assigned the new pesticide and the other half continue using an alternative pesticide. The crops are compared after two seasons. 4. Random homeowners in a particular city are divided into two groups, those that currently use solar panels in their homes and those that do not. All participants are surveyed to determine whether electric bills are lower for those with solar panels. 5. A cancer study began by surveying male patients between the ages of 35 and 55 at a local hospital about their exercise routine. The health of these men is tracked over 10 years to determine the effect of exercise on lowering the risk of cancer. 6. Researchers studying how exercise affects cholesterol sample 50 people who exercise regularly and 50 who do not. Blood was drawn from each person and serum cholesterol was measured.

1. Experiment 2.observational study 3.experiment 4. observational study 5.observational study 6. observational study

Select the best definition of population and sample.

A population is the complete group under study. A sample is a sub-collection of members of the population from which the data are actually collected.

Consider the experiments. Experiment 1: A study is done to determine which of two fuel mixtures allows a rocket to travel farther over a period of time. Rocket A, which requires additional equipment to keep it stable, is used to test one fuel mixture, and rocket B is used to test the other. Both rockets are identical aside from their mass. The results indicate that rocket B traveled farther than rocket A over the same period of time. Experiment 2: A double-blind experiment is performed to test whether a new drug is effective in lowering blood pressure. A random sample of subjects with high blood pressure is assigned to two groups. One group receives the new drug and the other group does not. Neither group is permitted to take any other medications during the experiment or to change their lifestyles in any way. The results of the experiment show that the drug is effective in lowering blood pressure.

Identify the experiment in which confounding occurs and the reason for its occurrence. Experiment 1 has a cofounding variable related to the mass of the rockets. Any variation in mass may cause a discrepancy in the distance traveled.

A health care provider wants to rate its members' satisfaction with physical therapy. A questionnaire is mailed to 800 members of the health plan selected at random from the list of members who were prescribed physical therapy in the past 12 months. Only 212 questionnaires are returned.

What is the intended population in this study? Be careful: What group does the health care provider want information about? Answer: all members who received physical therapy in the past 12 months What is the sample? Be careful: From what group does the provider actually obtain information? Answer: the 212 members who returned the questionnaire

Suppose a survey of 1000 students is obtained from a college whose population is 10,000 students. The sample was obtained by selecting at random from the population without replacement, meaning that no student could be selected twice.

a sample that is not random because the probability of being selected changes as members of the population are selected.

Select the correct definition of an experiment from the choices below.

a. A study where subjects are given treatments and their responses are measured and recorded. b.An official survey given to every member of a population in order to collect information about each individual. c. A group drawn from a population that is used in studies to gather information about the population. d. A study where data are collected and recorded by observing subjects, but no treatments are given to the subjects in the study. Answer is A Explanation: Experiment try to find affect more on the subjects from cause of the relationship from something.

select the correct definition of an observational study

a. study where subjects are selected based on convenience to the researcher. b. study where researchers manipulate variables and impose treatments on the subjects in the study ,then measure and record responses of the subjects c. study where researchers measure and record data about the subjects in study, but do not apply any treatments to the subjects or manipulate any variables. D. study that rejects or fails to reject a statistical hypothesis about a population parameter. E. A study where neither the subjects nor the researchers know what treatments are being administered to which subjects. answer is C explanation: the observational study just observes and record data does nothing to affect the variables in any way.

A January 2010 SurveyUSA poll asked a random sample of adults living in the state of Washington the question: "State lawmakers are considering making marijuana possession legal. Do you think legalizing marijuana is a good idea or a bad idea?" Of the 500 adults interviewed, 285 said "good idea." What percent of respondents seemed to support the idea of legalizing marijuana? Enter your answer rounded to one decimal place

divide 285/500 x 100 = 57 %

A study in El Paso, Texas, looked at seat belt use by drivers. Drivers were observed at randomly chosen convenience stores. After they left their cars, they were invited to answer questions that included questions about seat belt use. In all, 75% said they always used seat belts, yet only 61.5% were wearing seat belts when they pulled into the store parking lots.

select the correct explanation of the reason for the bias observed in responses to survey.