Lesson 11.3: Collecting Data - Surveys, Experiments, and Observational Studies Learning Goal: (S-IC.B.3) I can recognize the purposes of and differences among sample surveys, experiments, and observational studies. I can explain how randomization relates to each. Essential Question: What kinds of statistical research are there and which ones can establish cause-and-effect relationships between variables? Homework Discussion HW #24 BI 614 #5-20

Recognizing Different Forms of Statistical Research Statistical research takes various forms depending on what the purpose of the research is: to measure a variable in a population, (Survey) to see if there is evidence of an association between two variables (Observational Studies) to determine whether one variable actually influences another variable. (Experiments) to reproduce the conditions of a situation or process using a model so that the simulated outcomes closely match the real-world outcomes. (Simulation)

Suppose a graduate school researcher is considering three studies related to math and music. Explore: Involves asking a random sample of high school students in a large school district whether they listen to music while doing math homework. 1st Study: Involves asking a random sample of students at a large university whether they are majoring in math and whether they also play a musical instrument or sing. 2nd Study: Involves a group of adult participants where half will be randomly assigned either to listen to classical music for 15 minutes before taking a logical reasoning test or to listen to white noise for 15 minutes before taking the same test. 3rd Study:

Group Consensus 1. Which study appears to look for an association between two variables without actively manipulating either one? What are those variables? 2nd study; variables: whether student has math ability and whether student has musical ability 2. Which study appears to be looking for evidence that one variable actually influences another variable? What are those variables, and which one is manipulated to see if it influences the other? 3rd study; variables: type of sound being played and the listener's performance on the logical test; type of sound is being manipulated to see if it influences listener's performance on the test 3. Which study appears to be simply measuring a variable in a population? What is that variable? 1st study; variable: listening to music while doing math homework

Group Consensus 1. Which study appears to look for an association between two variables without actively manipulating either one? What are those variables? 2. Which study appears to be looking for evidence that one variable actually influences another variable? What are those variables, and which one is manipulated to see if it influences the other? 3. Which study appears to be simply measuring a variable in a population? What is that variable?

Detecting Errors in Surveys A survey measures characteristics of interest about a population using a sample selected from the population. recall a sample needs to be representative of the population in order for the measurements obtained to be accurate random sampling is generally the best way to ensure representation Sources of Errors in Surveys Biased Questions: The wording of questions in a survey can influence the way people respond to questions. Avoid questions that: encourage a particular response do not provide enough information to give an accurate opinion are too sensitive to answer truthfully address more than one issue Interviewer Effect: If an interviewer asks the questions in a survey, the person being interviewed may give inaccurate responses to avoid being embarrassed. Non-response: Some people may be difficult to contact, or they may simply refuse to participate once contacted. If non-response rates are higher for certain subgroups of a population, then those subgroups will be underrepresented in the survey results.

Explain why the results of each survey are likely to be inaccurate, and then suggest a way to improve the accuracy of the survey. Group Consensus The owner of a business conducts interviews with a random sample of employees to have them rate how satisfied they are with their jobs. In a random sample of town residents, a survey asks, “Do you agree that our school cafeteria should switch to a healthier menu?" A teacher conducts one-on-one interviews with a random sample of her students to get feedback on her teaching methods. In a random sample of people, a survey asks, "Should the town build a playground and a dog area in the park on Main Street?"

What are your thoughts? Are biased questions in a survey always intentional on the part of the person designing the survey? Many surveys are conducted over the telephone. How could using only landline phones to conduct a survey affect the outcome?

Distinguishing Between Observational Studies and Experiments In an observational study, researchers determine whether an existing condition, called a factor, in a population is related to a characteristic of interest. For instance, an observational study might be used to find the incidence of heart disease among those who smoke. In the study, being a smoker is the factor, and having heart disease is the characteristic of interest. In an experiment, researchers create a condition by imposing a treatment on some of the subjects of the experiment For instance, an experiment might be conducted by having some people with eczema take a vitamin E pill daily, and then observing whether their symptoms improve. In the experiment, taking the vitamin E pill is the treatment, and improvement of symptoms is the characteristic of interest. Which of these do you think is preferred by researchers? Why? What is an example of a situation for which an observational study would be better than an experiment?

Determine whether each research study is an Determine whether each research study is an observational study or an experiment. Identify the factor if it is an observational study or the treatment if is an experiment. Also identify the characteristic of interest. Group Consensus Researchers measure the cholesterol of 50 subjects who report that they eat fish regularly and 50 subjects who report that they do not eat fish regularly. Researchers have 100 subjects with high cholesterol take fish oil pills daily for two months. They monitor the cholesterol of the subjects during that time. Researchers monitor the driving habits of 80 subjects in their twenties and 80 subjects in their fifties for one month by using a GPS device that tracks location and speed.

What are your thoughts? Suppose the researchers in the first scenario find that considerably more people who eat fish regularly have normal cholesterol levels than those who do not eat fish regularly. Is it reasonable to conclude that eating fish regularly has an effect on cholesterol? Explain.

Examples: Identify the method of data collection each situation describes. A researcher records whether people at a gas station use hand sanitizer. A landscaper fertilizes 20 lawns with a regular fertilizer mix and 20 lawns with a new organic fertilizer. The landscaper then compares the lawns after 10 weeks and determines which fertilizer is better. Members of a student council at your school ask every eighth student who enters the cafeteria whether they like the snacks in the school’s vending machines. A researcher uses a computer program to help determine how fast an influenza virus might spread within a city.

Practice to Strengthen Understanding Explain why the survey question may be biased or otherwise introduce bias into the survey. Then describe a way to correct the flaw. Exit Ticket: In a random sample of town residents, a survey asks, "Are you in favor of a special tax levy to renovate the dilapidated town hall?" A child asks, "Do you support the construction of a new children's hospital?" Practice to Strengthen Understanding HW#25 BI p615 #21-33