S ECTION 5.2 – D ESIGNING E XPERIMENTS. V OCAB Experimental Units – Individuals on which the...
-
Upload
imogen-norris -
Category
Documents
-
view
213 -
download
0
Transcript of S ECTION 5.2 – D ESIGNING E XPERIMENTS. V OCAB Experimental Units – Individuals on which the...
VOCAB
Experimental Units – Individuals on which the experiment is being
done.
Subjects – Human beings for experimental units.
Treatment – Specific condition applied to an experimental
unit.
Factors – Explanatory variables.
VOCAB
Placebo – Dummy Pill/Treatment.
Placebo Effect – Psychological effect of responding favorably to
any perceived treatment.
Control Group – Group receiving no treatment or placebo
treatment.
Experimental Group – Group receiving experimental treatment.
THREE BASIC PRINCIPLES OF EXPERIMENTAL DESIGN
1. Control – Control the effects of lurking variables on the
response, most simply by comparing 2 or more treatments.
2. Randomize – Use chance to assign units to treatments.
3. Replicate – Use the same treatment on many units to reduce
chance variation.
COMPLETELY RANDOMIZED DESIGN
A completely randomized design happens when all experimental units are allocated at random among all treatments.
EXAMPLE #1:
What is the best way to answer each of the questions below: an experiment, a sample survey, or an observational study? Explain your choices.
1. Are people generally satisfied with how things are going in the country right now?
o Survey, no treatment, and cannot tell if someone is satisfied by observing them.
EXAMPLE #1:
2. Do college students learn basic accounting better in the classroom or using an online course?
o Experiment, has two treatment that results can be compared.
3. How long do your teachers wait on the average after they ask their class a question?
o Observational Study, no treatment given, and responses to survey questions would be bias.
EXAMPLE #2:
New varieties of corn with altered amino acid content may have higher nutritional value than standard corn, which is low in the amino acid lysine. An experiment compares two new verities, called opaque-2 and floury-2, with normal corn. The researchers mix corn-soybean meal diets using each type of corn at each of three protein levels, 12% protein, 16% protein, and 20% protein. They feed each diet to 10 one-day-old male chicks and record their weight gains after 21 days. The weight gain of the chicks is a measure of the nutritional value of their diet.
EXAMPLE #2:
What are the experimental units and the response variable in this experiment?
Experimental Units – one-day-old male chicks
Response Variable – weight gain
EXAMPLE #2:
How many factors are there? How many treatments? How many experimental units does the experiment require?
Factors – 2, amino acid content and protein level.
Treatments – 6, 2 different types of amino acid with 3 levels of protein for each type.
Number of experimental units – 60, 6 treatments with 10 chicks each.
EXAMPLE #2: Use a diagram to describe a completely
randomized design for this experiment.
60 Chicks
Group 110 Chicks
Group 210 Chicks
Group 310 Chicks
Group 410 Chicks
Group 510 Chicks
Group 610 Chicks
Treatment 1Opaque-2, 12% PTreatment 2Opaque-2, 16% PTreatment 3Opaque-2, 20% PTreatment 4Floury-2, 12% P
Treatment 5Floury-2, 16% P
Treatment 6Floury-2, 20% P
Compare Weight Gains
Ran
dom
as
sign
men
ts
MORE VOCAB
Double Blind– Neither subject nor the people that have contact
with them know the treatment being used. Matched-Pairs Design –
Compare just two treatments. A design to compare two treatments through one-sample procedures.
Block – A group of experimental units that are known to
be similar in some way that is expected to affect the response to the treatments.
Block Design– In a block design, the random assignment of units
to treatments is carried out separately within each block.
EXAMPLE #1:
Do consumers prefer the taste of a cheeseburger from McDonald’s or from Wendy’s in a blind test in which neither burger is identified? Describe briefly an experiment that could be used to answer this question.
o Make the experiment a combination of double-blind and matched pairs procedures. The source of the cheeseburger can’t be know ahead of time by the tasters, it could bias their opinion. Each subject must taste both cheeseburgers in order to identify with one they prefer.
EXAMPLE #2:
Is the number of days a letter takes to reach another city affected by the time of day it is mailed and whether or not the zip code is used? Briefly describe the design of a two-factor experiment to investigate this question. Be sure to specify the treatments exactly and to tell how you will handle lurking variables such as day of the week on which the letter is mailed.
EXAMPLE #2: Use a diagram to describe this experiment.
X Pieces of Mail
Group 1X/n Mail
Group 2X/n Mail
Group 3X/n Mail
Group 4X/n Mail
Group n-1X/n Mail
Group nX/n Mail
Treatment 1Zip given, Time 1Treatment 2Zip given, Time 2Treatment 3Zip given, Time 3Treatment 4No Zip, Time 1
Treatment n-1No Zip, Time 2
Treatment nNo Zip, Time 3
Compare number of days