Do Now- Identify the sampling method (Cluster or stratified) Instructors teaching research methods are interested in knowing what study techniques their students are utilizing. Rather than assessing all students, the researchers randomly select 10 students from each of the sections to comprise their sample. Instructors teaching research methods are interested in knowing what study techniques their students are utilizing. Rather than assessing all students, the researchers randomly select 2 sections and research all the students in those 2 sections to comprise their sample.

Observational Studies vs. Experiments Lesson 4.2 Day 1 Observational Studies vs. Experiments

Objectives Explain the concept of confounding and how it limits the ability to make cause-and-effect conclusions. Distinguish between an observational study and an experiment, and identify the explanatory and response variables in each type of study. Identify the experimental units and treatments in an experiment.

Complete #1-5 with your groups

Debrief

#5 Randomly choose 100 juniors to be a part of the experiment. Randomly split them up so half of them take the class and the others don’t. After the course is over all 100 juniors take the SAT. We compare the average scores of the groups.

Definitions Observational studies: no treatments imposed, we only observe Experiments: treatments imposed, allows for causation

Definitions Explanatory Variable: used to predict More than 1 are called factors Factors have levels Response variable: outcomes

Definitions Treatment: what is done to participants Experimental Units: what/who the treatment is imposed on Confounding variables: variables not controlled for that affect results

Random sample vs random assignment Random Sample: A random sample should be representative of the population from which it was taken, so a random sample allows us to generalize our conclusion to the population. In the SAT prep class example, we have 44 student volunteers.  Thus we cannot generalize our conclusion to all students.  Instead we can only make a conclusion for these 44 students or other students like the ones who volunteered for the experiment.

Random sample vs random assignment Random Assignment: Random assignment hopefully will equally distribute the various levels of the confounding variables into the treatment groups, so that only difference between groups is the treatment.  If there is a significant difference between the groups, the random assignment allows us to conclude that the treatment caused the difference.

Check your understanding Do Now: Complete check your understanding from yesterday’s worksheet

Designing Experiments Lesson 4.2 Day 2 Designing Experiments

Objectives Describe the placebo effect and the purpose of blinding in an experiment. Describe how to randomly assign treatments in an experiment using slips of paper, technology, or a table of random digits. Explain the purpose of comparison, random assignment, control, and replication in an experiment.

Would you fall for that? Video

#2 There is nothing to compare to. → Control Group Sugar might increase pulse rate. → Control other variables People know they’re getting caffeine so it could be placebo effect. →Blinding

Design an experiment Take the students and randomly split them into 2 groups. Give one group regular coke and the other caffeine-free. Compare their change in heart rate. Create a diagram for this experiment.

Do Now What are the effects of repeated exposure to an advertising message? The answer may depend on both the length of the ad and on how often it is repeated. An experiment investigated this question using 120 undergraduate students who volunteered to participate. All subjects viewed a 40-minute television program that included ads for a digital camera. Some subjects saw a 30-second commercial; others, a 90-second version. The same commercial was shown either 1, 3, or 5 times during the program. After viewing, all the subjects answered questions about their recall of the ad, their attitude toward the camera, and their intention to purchase it. A) For the advertising study, identify the experimental units or subjects, explanatory and response variables, and the treatments.

Definitions Control Group: used to provide baseline data for comparison. Blinding: When subjects (single-blind) and/or experimenters (double-blind) who interact with subjects are unaware of what treatment was assigned. Placebo Effect: When a fake treatment works.

Double-Blind: there should be another researcher who would know who received what treatment.  However, even if there was not, the researcher could cover the pill bottles and mix them up.  Then they could dispense treatment and uncover the bottles later to see which group had each treatment.

4 key principles of experiments Comparison - 2 or more treatments Random Assignment – use a chance process to assign treatments to experimental units Control - keep all other variables besides treatments constant Replication: using enough experimental units to distinguish differences.

Do Now Complete #1a and d on check your understanding on lesson 4.2 day 2 worksheet

Some more ideas to note… The Language of Experiments Suppose that we thought that the temperature of the Coca Cola might also effect the pulse rate.  So not only are we using Coke and Caffeine Free Coke, we are also testing it at 35 degrees, 50 degrees, and 70 degrees. Factor: A variable that is manipulated and may cause a change in the response variable (presence of caffeine and temperature). Levels: The different values of the factors.  The factor “presence of caffeine” has two levels (yes and no) and the factor “temperature” has three levels (35, 50, and 70 degrees). Treatments: A specific condition applied to the individuals in an experiment.  In this experiment, there are 6 treatments: (Yes, 35), (No, 35),  (Yes, 50), (No, 50), (Yes, 70), (No, 70).

Do Now What are the effects of repeated exposure to an advertising message? The answer may depend on both the length of the ad and on how often it is repeated. An experiment investigated this question using 120 undergraduate students who volunteered to participate. All subjects viewed a 40-minute television program that included ads for a digital camera. Some subjects saw a 30-second commercial; others, a 90-second version. The same commercial was shown either 1, 3, or 5 times during the program. After viewing, all the subjects answered questions about their recall of the ad, their attitude toward the camera, and their intention to purchase it. A) For the advertising study, identify the experimental units or subjects, explanatory and response variables, and the treatments. B) Identify the number of factors and amount of levels each factor has.

Check your understanding

Randomized Block Design Lesson 4.2 Day 3 Randomized Block Design

objectives Describe a completely randomized design for an experiment. Describe a randomized block design and a matched pairs design for an experiment and explain the purpose of blocking in an experiment.

Complete #1 with your group

Complete #2 with your group Complete #2 with your group. Put your diagram/outline on the provided whiteboard for me to check. Try your best!

Discuss #3 with your group and then we’ll discuss as a class.

Do Now What are the effects of repeated exposure to an advertising message? The answer may depend on both the length of the ad and on how often it is repeated. An experiment investigated this question using 120 undergraduate students who volunteered to participate. All subjects viewed a 40-minute television program that included ads for a digital camera. Some subjects saw a 30-second commercial; others, a 90-second version. The same commercial was shown either 1, 3, or 5 times during the program. After viewing, all the subjects answered questions about their recall of the ad, their attitude toward the camera, and their intention to purchase it. A) For the advertising study, identify the experimental units or subjects, explanatory and response variables, and the treatments. B) Identify the number of factors and amount of levels each factor has.

#3 debrief Notice that the matched pairs design is really just a fancy version of a block design, where each block is of size 2 (two students paired with similar GPAs).

Definitions Block- group of experimental units that are known to be similar Randomized Block Design – separate subjects into blocks and then randomly assign to treatments within each block

definitions Matched pairs - experiment used to compare two treatments that uses blocks of size 2 Two very similar experimental units are paired and then randomly assigned to a treatment.

Which variable should be used for blocking? Why block? Should we create blocks of Juniors and Seniors?  Blocks of males and females?  Blocks of high GPA and low GPA? Which variable?  Choose the one that is most strongly associated with the response variable.  We think grade level is the variable that is most strongly associated with differences in SAT scores. Why block? To reduce the variability in the response variable (SAT score).  The variability of SAT scores should be less in each block then it would be for the whole group.  This can help make it easier to determine if results are statistically significant (increase power).  

The thinking and reasoning here is very similar to making the choice of variable to use when doing a stratified random sample (like the choice of stratifying by row in the Justin Timberlake lesson).

Check your understanding

Are ELEPHANTS REALLY AFRAID OF MICE?

Answer the following on your whiteboard with your group 1) Identify the following: experimental units response variable treatment explanatory variables or factors 2) Was there a control group? Why?

Read the provided article In your groups, read your assigned article and identify the: experimental units response variable treatment and factors from the study.  Be prepared to summarize your article and share your answers with the class