1. Do now: Identify the population and sample

2. Collecting Data-Conducting an experiment
Module 6 Summer 2016

3. Experiment
Purpose it to find cause and effect relationship between 2 variables
Explanatory and response variables
Confounding variables

4. Control the confounding variable
Direct control: The experiments attempts to control all of the confounding variables
Random Assignment: Uses random chance to assign participants to treatment groups. Helps balance the other variables.
Control Groups: One groups is exposed to the treatment and one is not.
Placebo: “fake”
Blinded study:
Single Blinded: Either the subject or those who interact with them know who is receiving the treatment
Double Blinded: Neither the subject or those who interact with them know which treatment a subject received.
Direct control: Give all students the same Pre test, the same SAT test, the same amount of time on the test, given in the same environment.
Placebo: If we give one group a pill and the other group no pill they are not treated equally.
Placebo effect: The response to a dummy treatment

5. Parts of an experiment
Treatment: The specific condition applied to the individuals
Experimental units: The smallest collection of individuals to which treatments are applied
Response Variable: The outcome in an experiment
Explanatory variable: The variable that one changes

6. A lousy situation
A study published in the New England Journal of Medicine (March 11, 2010) compared two medicines to treat head lice: an oral medication called ivermectin and a topical lotion containing malathion. Researchers studied 812 people in 376 households in seven areas around the world. Of the 185 households randomly assigned to ivermectin, 171 were free from head lice after 2 weeks compared with only 151 of the 191 households randomly assigned to malathion.
Problem: Identify the experimental units, explanatory and response variables, and the treatments in this experiment.

7. A lousy treatment Solution:
The experimental units are the 376 households, not the 812 people, because the treatments were assigned to entire households, not separately to individuals within the household.
The explanatory variable is type of medication
response variable is whether the household was lice-free.
The treatments were ivermectin and malathion.

8. Growing Tomatoes
Does adding fertilizer affect the productivity of tomato plants? How about the amount of water given to the plants? To answer these questions, a gardener plants 24 similar tomato plants in identical pots in his greenhouse. He will add fertilizer to the soil in half of the pots. Also, he will water 8 of the plants with 0.5 gallon of water per day, 8 of the plants with 1 gallon of water per day, and the remaining 8 plants with 1.5 gallons of water per day. At the end of 3 months, he will record the total weight of tomatoes produced on each plant. Problem: Identify the experimental units or subjects, explanatory and response variables, and the treatments.

9. Growing tomatoes Solution:
The experimental units are the tomato plants.
The two explanatory variables (factors) are whether fertilizer is applied and amount of water.
The response variable is the weight of tomatoes produced.
There are 6 treatments: (1) fertilizer, 0.5 gallon; (2) fertilizer, 1 gallon; (3) fertilizer, 1.5 gallons; (4) no fertilizer, 0.5 gallon; (5) no fertilizer, 1 gallon; (6) no fertilizer, 1.5 gallons.

10. How to buy Happiness
Watch the short TED talk “How to Buy Happiness” by Michael Norton at
Problem: What are the explanatory variables? What are the treatments?

11. How to buy happiness
Explanatory Variables: amount of money and how it is spent.

12. Ticket out the door?
Music students often don’t evaluate their own performances accurately. Can small-group discussions help? The subjects were 29 students preparing for the end-of-semester performance that is an important part of their grade. The 15 students in one group each video-taped a practice performance, evaluated themselves, and then discussed the tape with a small group of other students. The remaining 14 students watched and evaluated their final performance more accurately.
Describe a completely randomized design for this experiment.
What is the purpose of the control group?
Randomly assign the 29 students to 2 different groups: evaluating their performance in small groups and evaluating their performance alone. The response variable will be their accuracy of their final performance evaluations.
Provide a baseline for comparison.