Lesson 11.4: Experimental Design 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: How can you use an experiment to test a conjecture? Homework Discussion HW#25 BI p615 #21-33

Identifying Control Groups and Treatment Groups in Experiments Recall from yesterday: a comparative observational study can suggest a relationship between variables (correlation), it cannot establish a cause-and-effect relationship this is due to confounding variables In an experiment, randomization can remove the problem of a confounding variable by distributing the variable among the groups being compared so that its influence on the groups is more or less likely. The best way to establish a cause-and-effect relationship between two variables is through a randomized comparative experiment where subjects are randomly divided into two groups: the treatment group, which is given the treatment, and the control group, which is not

Identify the treatment, characteristic of interest, control group, and treatment group for the given experiment. Assume all subjects of the research are selected randomly. Group Consensus To see whether zinc has an effect on the duration of a cold, researchers have half of the subjects take tablets containing zinc at the onset of cold symptoms and the other half take tablets without any zinc. The durations of the colds are then recorded. To see whether regular moderate exercise has an effect on blood pressure, researchers have half of the subjects set aside 30 minutes daily for walking and the other half not do any walking beyond their normal daily routines. The subjects also take and record their blood pressure at the same time each day.

Identify the treatment, characteristic of interest, control group, and treatment group for the given experiment. Assume all subjects of the research are selected randomly. Your Turn To see whether reviewing for a test with a classmate improves scores, researchers ask half of the subjects to study with a classmate and the other half to study alone. The test scores are then recorded. What Are Your Thoughts? An experiment involves testing the effectiveness of a new drug. Why does giving the subjects in the control group a pill that does not contain the drug make the results more valid than if the subjects in the control group did not take any pill at all?

Evaluating Media Reports of Statistical Research When evaluating media reports of statistical research, you should judge any reported conclusions on the basis of how the research was conducted. Questions to consider: Is the research a survey, an observational study, or an experiment? Was randomization used in conducting the research? Does the report include the details of the research, such as sample size, statistics, and margins of error? details help you judge how much confidence to have in the results of the research or how much importance to place on the results.

Caring Doctors Shorten and Ease the Common Cold Group Consensus Evaluate the articles by answering the following questions. Is this a survey, an observational study, or an experiment? How do you know? Was randomization used in the research? If so, how? What details of the research does the article include? Is any important information missing? Researchers have found that among patients with colds, those who gave their perfect scores on a questionnaire measuring empathy have colds that did not last as long and were less severe. Empathy on the part of doctors included making patients feel at ease, listening to their concerns, and showing compassion. A total of 350 subjects who were experiencing the onset of a cold were randomly assigned to one of three groups: no doctor-patient interaction, standard interaction, and enhanced interaction. Only subjects in the third group saw doctors who had been coached on being empathetic. Caring Doctors Shorten and Ease the Common Cold

Fitness in Teen Years May Guard Against Heart Trouble Later A study of almost 750,000 Swedish men suggests people who are aerobically fit as teenagers are less likely to have a heart attack later in life. Each 15 percent increase in the level of aerobic fitness as a teenager is associated with an 18 percent reduced risk of a heart attack 30 years later. Overall, teens and young adults who participate in regular cardiovascular training have a 35 percent reduced risk of a heart attack later in life. The researchers analyzed medical data from men drafted into the nation’s army, which requires a test of aerobic fitness at the time of induction. National health registers provided information on heart attacks the men had later in life. Fitness in Teen Years May Guard Against Heart Trouble Later

Designing an Experiment or Observational Study Explain whether the following research topic is best investigated through an experiment or observational study. Then describe the design of the experiment or observational study. You want to know whether vigorous exercise in older people results in longer life. You want to know whether flowers sprayed twice per day with a mist of water stay fresh longer than flowers that are not sprayed.

Analyzing Experimental Designs When analyzing experimental designs consider: sample size and replication Example: A pharmaceutical company wants to test the effectiveness of a new chewing gum designed to help people lose weight. Identify a potential problem, if any, with each experimental design. Then describe how you can improve it. The company identifies 10 people who are overweight. Five subjects are given the new chewing gum and the other 5 are given a placebo. After 3 months, each subject is evaluated and it is determined that the 5 subjects who have been using the new chewing gum have lost weight. The company identifies 10,000 people who are overweight. The subjects are divided into groups according to gender. Females receive the new chewing gum and males receive the placebo. After 3 months, a significantly large number of the female subjects have lost weight. The company identifies 10,000 people who are overweight. The subjects are divided into groups according to age. Within each age group, subjects are randomly assigned to receive the new chewing gum or the placebo. After 3 months, a significantly large number of the subjects who received the new chewing gum have lost weight.

Practice to Strengthen Understanding Exit Question: What is the difference between an experiment and an observational study? Practice to Strengthen Understanding HW#26 p623 #3-12