Association and Causation Math 075 Fall 2016

Agenda Entry ticket Introduction to association and causation In class Activity Exit Ticket Homework-Part 1: bring in an example of a association and a causation from an article, newspaper article, etc. Be prepared to explain why each example is a association or causation in class.

Entry Ticket: Association and Causation Explain the joke in this cartoon. 2. Write another example of the joke.

Association When two variables are related Turn and Talk: Describe how these two variables are related.

Causation When one variable causes another variable to change. A  B Example: As you run faster, the number of calories you are burning increases. Other Examples?

1.1 Types of Statistical Studies

Variables Explanatory: The variable that is being manipulated Response: The variable we are measuring

Observational Study Vs. Experiment Observational study: Observes individuals (population) and measures variables of interest. Experiment: Intentionally manipulates one variable (explanatory) in an attempt to cause and effect on another variable (response). The purpose to create a cause-and-effect relationship.

Population Vs. Sample We’d like to know about an entire population of individuals, but examining all of them is usually impractical, if not impossible. We settle for examining a smaller group of individuals—a sample—selected from the population.

Population Vs. Sample Sampling is a natural thing to do. Think about sampling something you are cooking—you taste (examine) a small part of what you’re cooking to get an idea about the dish as a whole.

Checking for Understanding The age of every third person entering a clothing store.   The amount of energy collected from every wind turbine on a wind farm. The annual salary of each pharmacist at a pharmacy.

Checking for Understanding The cholesterol level of 20 patients in a hospital with 100 patients.   The soil contamination levels at 10 locations near a landfill. The revenue of each of the 30 companies in the Dow Jones Industrial Average.

Observational Study or Experiment Does reducing screen brightness increase battery life in laptop computers? To find out, researchers obtained 30 new laptops of the same brand. They chose 15 of the computers at random and adjusted their screens to the brightest setting. The other 15 laptops screens were left at the default setting-moderate brightness. Researches then measure how long each machine’s battery lasted. Is this an observational study or experiment? Justify your answer. Experiment because the treatment was imposed on the laptops.

Observational Study or Experiment An educator wants to compare the effectiveness of computer software for teaching biology with that of a textbook presentation. She gives a biology pretest to each of a group of high school juniors, then randomly divides them into two groups. One group uses the computer, and the other studies the text. At the end of the year, she tests all students again and compares the increase in biology test scores in the two groups. . Is this an observational study or experiment? Justify your answer. Experiment because students were assigned randomly to the different teaching methods

Observational Study or Experiment One study of cell phones and the risk of brain cancer looked at a group of 469 people who have brain cancer. The investigators matched each cancer patient with a person of the same age, gender, and race who did not have brain cancer, then asked about the use of cell phones. Results “Our data suggest that the use of handheld cellular phones is not associated with the risk of brain cancer.” Is this an observational study or experiment? Justify your answer. Observational because the researchers did not assign people to either use or not use cell phones.

Observational Study or Experiment A study of child care enrolled 1364 infants and followed them through their sixth grade year in school. Later, the researcher published an article in which they stated that “the more time children spent in child care from birth to age four-and-a-half, the more adults tended to rate them, both at age four-and-a-half and kindergarten, as less likely to get along with others, as more assertive, as disobedient, and as aggressive. Is this an observational study or experiment? Justify your answer. Observational because children weren’t assigned to different amounts of child care.