UNIT 1: Scientific Foundations of Psychology
PART II: Research Methods: Thinking Critically With Psychological Science
6-1 Explain what it means when we say two things are correlated, and describe positive and negative correlations.
6-2 Explain illusory correlations and regression toward the mean.
6-3 Discuss why correlations enable prediction but not cause-effect explanations.
6-4 Describe the characteristics of experimentation that make it possible to isolate cause and effect.
Learning Targets
What does it mean when we say �two things are correlated?
a measure of the extent to which two factors
vary together, and
how well either factor predicts the other.
So for instance…
What is the difference between a �positive correlation and a �negative correlation?
positive correlation
Two sets of data tend to rise or fall together
Such as… college graduation and income levels. Those who complete college (rise) tend to earn more money (rise).
negative correlation
One set of data rises while the other falls
Such as… age and amount of nightly sleep. As we get older (rise) the amount of sleep we get decreases (fall).
Which of the following is an example of negative correlation?
1. What Would You Answer?
How do we measure correlations?
The correlation coefficient: a statistical index of the relationship between two variables.
Variables that are positively correlated are measured
Variables that are negatively correlated are measured
from r = -.01 to -1.0.
Note that correlation coefficients are expressed
as r values.
TRY IT
What would you estimate the correlation coefficient to be in these cases? �Closer to r = +1.0 or -1.0?
The relationship between drinking and driving and auto fatalities?
The connection between stress and disease?
The relationship between the heat outside and the use of air conditioners?
What is a scatterplot?
two variables.
What does a positive correlation �scatterplot look like?
The variables increase together or decrease together.
If one gets larger… so does the other.
The slope of the line goes UP
from left to right.
What does a negative correlation �scatterplot look like?
As one variable increases the other decreases.
If one variable gets smaller, the other gets larger.
The slope of the line goes DOWN
from left to right.
What does a “no relationship” �scatterplot look like?
As one variable increases or decreases, the other increases or decreases randomly.
There is no relationship between one and the other.
What is important to remember about correlation coefficients?
A correlation coefficient, which can range
from -1.0 to +1.0
reveals the extent to which two things relate.
The closer the score gets to +1 or -1, the
stronger the correlation.
The (+) or (-) sign before the number indicates whether the correlation is positive or negative.
The (+) or (-) sign indicates direction… not value.
Which of the correlation coefficients below expresses the strongest relationship between two variables?
+.76
-.91
1.2
0.01
TRY IT
What are illusory correlations?
Perceiving a relationship where none exists.
Or perceiving a stronger-than-actual relationship.
So for instance…
A sports fan wears a blue jersey the day her team wins, and she decides to wear that blue jersey on game days from now on although the jersey had no impact on the score.
What is regression to the mean?
The tendency for extreme scores or events to fall back toward the average.
So for instance…
How do correlations help us to �predict events?
Correlation does not imply causation.
Correlation does not prove causation.
Length of marriage
positively correlates with hair loss in
men. Does this mean that marriage
causes men to lose their hair (or that
balding men make better husbands)?
AP ® Exam Tip
Take note of how much emphasis
is put on this idea.
Correlation and association do not prove a
cause-effect relationship.
Correlation does not imply causation.
How can experiments establish �cause and effect?
Experiments enable researchers to isolate the effects of one or more factors by:
(1) manipulating the factors of interest
(2) holding constant (“controlling”) other factors.
What is an example of an experiment �that shows cause and effect?
Does breastfeeding lead to smarter children?
cause
effect
How were the groups assigned?
experimental group
Subjects receive
the treatment.
The pediatricians promoted breast feeding to the mothers in their group.
control group
Subjects do not receive the treatment.
The pediatricians provided normal care but did not promote breastfeeding.
How was the experiment conducted?
experimental group
At 3 months of age,
43% of the babies were being breastfed.
control group
At 3 months of age,
6% of the babies were being breastfed.
(Kramer et al, 2008)
What were the results?
At age 6,
when nearly 14,000 of the children were restudied, those who had been in the breast-feeding promotion
experimental group
had intelligence test scores
averaging six points higher than their
control condition counterparts.
What is random assignment?
Assigning participants
to experimental and
control groups
by chance, thus
minimizing preexisting differences
between the different groups.
Why does random assignment help �establish cause and effect?
In order to control confounding variables, experimenters randomly assign subjects to the experimental
and
control group.
What if all the babies in the experimental group, shared one specific trait that influenced intelligence?
What is the difference between random sampling and random assignment?
random sampling
Choosing a representative sample of the population being studied.
Allows the results to be generalized to the population as a whole.
random assignment
Assigning the participants to the experimental or control group by chance.
Minimizes pre-existing differences between the two groups.
How does using a blind procedure�help establish cause and effect?
single blind
The participants in the study are uninformed about the treatment, if any, they are receiving.
double blind
The participants and the researcher are uninformed about which group receives the treatment and which does not.
Controls for subject response bias and placebo effect.
Controls for experimenter and subject bias as well as placebo effect.
In a drug study, neither the participants nor the person distributing the pills knows who is receiving the new drug and who is receiving the placebo. This type of research design is said to be a(n) ______ study.
2. What Would You Answer?
What is the placebo effect?
A placebo is an inert treatment…like a pill without any medication inside.
The placebo effect causes experimental results simply from expectations or assumptions that medication is being taken.
Let’s look at the research on the �placebo effect…
Athletes have run faster when given a supposed performance-enhancing drug.
(McClung & Collins, 2007)
Decaf-coffee drinkers have reported increased
vigor and alertness—when they thought their
brew had caffeine in it.
(Dawkins et al., 2011)
People have felt better after receiving a phony
mood-enhancing drug.
(Michael et al., 2012)
What is the difference between an �independent and dependent variable ?
independent variable (IV)
In an experiment, the factor that is manipulated; the variable whose effect is being studied.
dependent variable
(DV)
In an experiment, the
outcome that is measured; the variable that may
change when the independent variable is manipulated.
IV given only to experimental group.
DV measured in both groups.
AP ® Exam Tip
The identification of
independent (IV) and dependent variables (DV)
is the single most likely concept to be tested
on the AP® exam.
Experiments are critical to psychology, and
independent and dependent variables
are critical to experiments.
Remember to use operational definitions to quantify variables on the FRQ section of the exam.
Consider these hypotheses from Module 5. Identify the IV and the DV in each instance.
Music helps plants grow.
Ginger tea helps reduce hyperactivity in teens
Eating junk food causes weight gain.
TRY IT
In an experiment to test the effects of room temperature on test performance, the independent variable is
3. What Would You Answer?
What is a confounding variable?
A factor
other than the factor being studied
that might influence a study’s results.
The key is that some unique factor must be present in one of the groups (experimental or control),
but not in the other.
A variable cannot be confounding if it occurs
to the same degree in both groups.
Random assignment is one method used to prevent confounding variables.
What are some examples of �confounding variables?
age
intelligence level
ethnicity
sex
political beliefs
What is experimental validity?
The extent to which a
test or experiment measures or
predicts what it is supposed to.
For instance… if you take a driving test and pass it, we should expect to see accurate driving skills from you.
The driving test would be considered a valid measure of your ability to drive.
Researchers surveyed 800 high school students enrolled in AP® Psychology to determine whether students with higher scores on anxiety scales had lower scores on standardized tests. Students with higher scores on anxiety scales were indeed found to have lower scores on standardized tests.
Explain how each of the following terms or phrases applies to the situation described above:
4. What Would You Answer?
Learning Target 6-1 Review
Explain what it means when we say
two things are correlated, and
describe positive and negative correlations.
Learning Target 6-1 Review cont.
Explain what it means when we say
two things are correlated, and
describe positive and negative correlations.
Learning Target 6-2 Review
Explain illusory correlations and
regression toward the mean
Learning Target 6-3 Review
Discuss why correlations enable prediction
but not cause-effect explanation
Learning Target 6-4 Review
Describe the characteristics of experimentation
that make it possible to isolate
cause and effect.
Learning Target 6-4 Review cont.
Describe the characteristics of experimentation
that make it possible to isolate
cause and effect.