Chapter 1: Thinking Critically with
Psychological Science
Aaron Biggar
AP Psychology
I. The Need for Psychological Science
98% Certainty
1. The area of the US in square miles?
2. The population of Afghanistan in 2001?
3. American battle deaths in Spanish-American War?
4. GM advertising budget in 1999?
5. Female officers in US Army in 2000?
98% Certainty
1. Area of US:
2. Afghan population:
3. Battle deaths:
4. GM advertising:
5. Female officers:
3.6 million sq. miles
26.8 million
385
$2.9 billion
9.953
I. The Need for Psychological Science
A. Limits of intuition and common sense
1. Hindsight bias
2. Overconfidence
I. The Need for Psychological Science
A. Limits of intuition and common sense
B. Scientific attitude
C. Scientific method
1. Theory & hypothesis
2. Operational definitions
3. Replication
4. Goals:
II. Description
II. Description
A. Case studies
B. Surveys (questionnaires & interviews)
1. Wording effects
72% interested in “plants & trees”39% interested in “botany”
62% whites agree “problems faced by blacks brought on by blacks themselves” (white interviewer)46% whites agree with black interviewer
A majority oppose an amendment “prohibiting abortions”A majority support “protecting the life of an unborn child”
1. Is the Mississippi River longer or shorter than 500 miles?
2. How many miles long is it?
1. Is the Mississippi River longer or shorter than 3000 miles?
2. How many miles long is it?
II. Description
A. Case studies
B. Surveys (questionnaires & interviews)
1. Wording effects
2. Samples & populations
a. False consensus & other biases
b. Random & representative techinques
II. Description
A. Case studies
B. Surveys (questionnaires & interviews)
C. Naturalistic observation & observer effects
III. Correlation
III. Correlation
A. Positive & negative
B. Scatterplots
III. Correlation
A. Positive & negative
B. Scatterplots
C. Correlation coefficient (r)
III. Correlation
A. Positive & negative
B. Scatterplots
C. Correlation coefficient (r)
D. Causation v. predictive value
Correlation between TV watching & GPA
III. Correlation
A. Positive & negativeB. ScatterplotsC. Correlation coefficient (r)D. Causation v. predictive value
E. Illusory correlationF. Order in random events
IV. Experimentation
IV. Experimentation
Purpose of an expt:
General hypothesis: food effects learning
Specific (operationalized) hypothesis: students who eat an oatmeal raisin cookie before class each day will have higher average scores on the semester final than students who don’t eat a cookie.
Eating cookies before class each day will lead to higher average scores.
Variables:Independent (IV)
Controlled by experimenterThe “cause” variable
Dependent (DV)Predicted by experimenterThe “effect” variable
Eating cookies before class each day will lead to higher average scores.
Groups (conditions): to establish different levels of the IV
Experimental groupExposed to IVGet cookie
Control groupNot exposed to IVNo cookie
What if kids get cookies and A’s?
Eating cookies before class each day will lead to higher average scores.
IV DV
Expt. Gp. Cookie 95%
Cntrl. Gp. No Cookie 82%
ConfoundingVariables
Environmental
Expectations
Individualdifferences
Random SamplingTo select participants from populationAllows you generalize results
Random AssignmentTo divide participants into groupsControls confounding variables
Eating cookies before class each day will lead to higher average scores.
IV DV
Expt. Gp. Cookie 95%
Cntrl. Gp. No Cookie 82%
85%
93%
Statistical Significance
p value
likelihood a result is caused by chance
can be no greater than 5%
p ≤ .05
Replication
Non-replicated results are preliminary.
Linus Pauling (1970). Vitamin C prevents colds.
IV DV
Expt. Gp. Vit C
Cntrl. Gp. Placebo
Expt. Gp.45%
Fewer colds
Experimental Design Terms
• Hypothesis• Operational definitions• Participant selection• IV & DV• Experimental & control groups• Confounding variables• Random assignment• Placebo control• Double blind procedure• Statistical significance (p value)• Replication
Quasi-experiments
• Men are better drivers than women.
• Cigarette smoking causes lung cancer.
V. Statistical Reasoning
V. Statistical Reasoning
A. Describing data
1. Frequency distributions
13 A+ 40 13 A+12 A 39 4 41% A 12 23 52% 12 A 11 39%
38 11 A- 11 10 11 A- 1411 A- 37 11 B+ 10 15 10 B+ 910 B+ 36 6 B 9 5 41% 9 B 12 45%9 B 35 4 31% B- 8 6 8 B- 8
34 5 C+ 7 2 7 C+ 28 B- 33 5 C 6 1 5% 6 C+ 2 11%7 C+ 32 4 C- 5 5 C- 36 C 31 3 19% D+ 4 2 4 D+
30 3 D 3 3% 3 D 3 5%5 C- 29 2 D- 2 2 D-4 D+ 28 F 1 0% 1 F 0%3 D 27 4 8% 0
26 12 D- 251 F 24 2%
<24 1
Multiple Choice
Essay
Composite
Mean=34.3SD=4.2
Mean=10.2SD=2.0
Mean=9.3SD=2.3
V. Statistical Reasoning
A. Describing data
1. Frequency distributions
2. Histograms & frequency polygons
0
10
20
30
40
50
A B C D
Grades
Per
cen
tag
e o
f st
ud
ents
Histogram
0
10
20
30
40
50
A B C D
Grades
Per
cen
tag
e o
f st
ud
ents
Frequency Polygon
V. Statistical Reasoning
A. Describing data
B. Measures of central tendency
43544
Mode=most common=4
Mean=arithmetic average=20/5=4
Median=middle score=4
Central Tendency 1968 TOPPS Baseball Cards
Nolan Ryan $1500
Billy Williams $8
Luis Aparicio $5
Harmon Killebrew $5
Orlando Cepeda $3.50
Maury Wills $3.50
Jim Bunning $3
Tony Conigliaro $3
Tony Oliva $3
Lou Pinella $3
Mickey Lolich $2.50
Elston Howard $2.25
Jim Bouton $2
Rocky Colavito $2
Boog Powell $2
Luis Tiant $2
Tim McCarver $1.75
Tug McGraw $1.75
Joe Torre $1.5
Rusty Staub $1.25
Curt Flood $1
With Ryan:Median=$2.50Mean=$74.14
Without Ryan:Median=$2.38Mean=$2.85
V. Statistical Reasoning
A. Describing data
B. Measures of central tendency
C. Measures of variation
1. Range
2. Variance & standard deviation
Standard DeviationPunt
Distance
36384145
Mean=160/4=40 yds
Deviationfrom Mean
-4-2+1+5
DeviationSquared
16 4 125
46
46/4=11.5=variance
std. dev.=
variance=
11.5=3.4 yds
V. Statistical Reasoning
A. Describing data
B. Measures of central tendency
C. Measures of variation
D. Characteristics of the normal curve
V. Statistical ReasoningA. Describing data
B. Measures of central tendency
C. Measures of variation
D. Characteristics of the normal curve
E. Inference
1. Does the sample represent the pop.?
a. Non-biased sample-good
b. Low variability-good
c. Larger samples-good
V. Statistical ReasoningE. Inference
1. Does the sample represent the pop.? 2. Are differences between groups
statistically significant?
a. Big differences-good
b. Low variability-good
c. Big groups-good
VI. FAQs
VI. FAQs
A. Can lab expts illuminate real life?
B. Does behavior depend on one’s culture?
C. Does behavior vary with gender?
D. Why do psychologists study animals?
E. Is it ethical to experiment on animals?
F. Is it ethical to experiment on people?
G. Is psychology free of value judgments?
H. Is psychology potentially dangerous?
VI. FAQs
F. Is it ethical to experiment on people? Yes, if the APA’s ethical guidelines are
followed.
1. Informed consent
2. Protection from harm
3. Confidentiality
4. Debriefing
How should participants be chosen?
• Good answers use and make clear your understanding of the terms “sample” and “population.”
• Good answers explain how to draw a random sample.
• Ex. “All the assembly line workers for a company could be the population. I would draw a random sample of 40 of them by picking names from a hat.”
Create operationalized hypothesis
• Good answers make an educated guess (“Workers who are complimented will work harder”)
• Good answers develop specific, measurable ways to define compliments and hard work.
• Ex. “10 compliments will be given at 4 specific times.” “Supervisors will give compliments from a pre-developed list.” “Hard work will be measured by using the number of items produced each hour.”
Identify IV & DV
• IV=compliments
• DV=work effort
• Do not propose a direction when stating the variable (“the DV is an increase in work.”)
• People are never the variables (“the IV is the people who get complimented.”)
Describe the groups
• Experimental group gets compliments.
• Control group doesn’t get compliments.
• Use the terms!
Confounding variables
• Do not confuse random assignment with random sampling.
• Be reasonable!!!
• “The company policy will be to have people sleep in a hotel with no TV or radio.”
• “I will provide a seminar on the importance of sleep.”
• “All workers must be paid the same.”