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Research Methods in Psychology
The Experiment
• Only research method capable
of showing cause and effect
Experimental Method
• Review Literature of Past Research
• Formulate Hypothesis
• Design Research/Study Method
(naturalistic observation, case
studies, surveys, experiments, etc)
• Collect the Data
• Analyze the Data
• Report the Findings (journal,
critique, replicate)
• Draw Conclusion or Theory on
Explanation of Findings
Hypothesis
• A statement about the relationship between two or more
variables
• Must be testable and refutable
• Instead of proving the hypothesis, science usually tries to
disprove a null hypothesis.
Null Hypothesis (H0):
opposite of hypothesis
Hypothesis Example:
Statistical Significance :
95% not due to chance
H0: Gender does not have an
effect on spatial ability
H1: Gender has an effect on
spatial ability
Variables
• Independent Variable (I.V.): manipulated by
experimenter
• Dependent Variable (D.V.): MEASURED
variable influenced by independent
• Operational definition
• Confounding/extraneous variables
Control Group
• No treatment or placebo
• Serves as basis for comparison
• Serves to eliminate alternative explanations
Population – The larger group of people
from which a sample is drawn
Sample: Representative of the population
Two ways to get sample
Random: Every member of the pop has = chance
Stratified: Sample is put together by picking a
group statistically equal to the population
Control Measures
• Counterbalance: controls for order effects
• Single-Blind: subject unaware of assignment
• Double-Blind: subject and experimenter unaware
of placement
• Randomization
– From population (sample)
– From assignment to groups (assignment)
Other Research Methods
Ex Post Facto (after the fact)
- Independent variable already present
- Not a true independent variable, no cause and effect
- Often used due to ethical concerns
Naturalistic Observation
- Natural setting: behavior is not interfered with or altered
Survey Method
- Gathers data on attitudes and behaviors.
Case Study
- Intense study of an individual
Statistics
Descriptive Statistics
Organize and summarize data
Central Tendency: mean, median, mode
Standard deviation: variation in data
Range: distance from smallest to largest
Inferential Statistics
Interpret data and draw conclusions
Used to test validity of hypothesis (t-test)
Standard Deviation
Statistical Significance
• Probability results are due to chance
• Inferential stats (t-test) are used to
check for either a 5% (p<.05) or 1%
(p<.01) level of significance.
Lottery tickets 14, 3, 27, 41, 18
1, 2, 3, 4, 5
Coin flips HHHHHHH or HHTHTHT
More likely?
Bell or Normal Curve
68% are within One standard deviation from mean
95% are within Two standard deviations from mean
Measures of Central Tendency
A Skewed Distribution
Skews
Correlation
A statistical value of the relationship between two variables
Positive Correlation
As one number increases, the other increases.
Ex: Study time to GPA
Negative Correlation
As one number increases, the other decreases.
Ex: Absences to GPA
No Correlation
Variables do not affect one another in a significant way
Ex: Height to GPA
Correlation Coefficient
• Ranges from -1.00 to 1.00
• Zero is no relationship
• -0.85 is a stronger relationship than .34
• CORRELATION IS NOT CAUSATION!!
(i.e. Just because two variables have a correlation
does not mean one causes the other)
CORRELATION IS NOT CAUSATION!!!
• People that floss everyday live 3 years longer than those that do not.
• Red wine drinkers live longer than those that do not drink red wine.
• As speed limits increased on America’s highways, the death rate went down.
• Women with breast implants commit suicide 3 times as often as those without
breast implants.
• Children who are played Mozart in the womb have higher IQ’s.
• Marijuana users in youth are more likely to have mental illness as adults.
• As ice cream sales increased, so did shark attacks.
• More TV’s per person in a country, the longer people live.
Illusory Correlation
Ways to Study the Brain
CT “cat” Scan: Computerized Axial Tomography
x-ray of the brain
MRI: Magnetic Resonance Imagingexcellent 3d image using magnetic fields
fMRI: Functional Magnetic Resonance Imaging
3d image and shows blood flow in brain
PET Scan: Positron Emission Tomography Scan
Uses radioactive material in blood to show brain
activity
EEG: Electroencephalograph- brain waves activity
CT Scans: An x-ray of the brain.
A CT scan is essentially a computerized assembly
of several x-ray images taken from a series of
different angles. With a CT, the resolution is much
better than conventional x-rays, and the detail
that can be seen is much greater.
CT Scans
PET
Scans
P
E
T
S
C
Normal Brain
ADHD Brain
A
N
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Brain Development
in First Year of Life
5
MRIs
3
Post Contrast sagittal T1 Weighted
M.R.I.
2
Section at the level of Foramen
Magnum
1
Answers
4
1. Cisterna Magna
2. Cervical Cord
3. Nasopharynx
Fig. 1.1 Post Contrast Axial MR Image of the brain
4. Mandible
5. Maxillary Sinus
Flaws in Research
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Sampling Bias
Overgeneralization
Placebo effect
Hawthorne/Barnum effect
Demand Characteristics
Experimenter Bias
Ethics in Research
• Participants are free to withdraw at any time
• No undo stress
• Subjects informed of significant factors that may
influence their willingness to participate
• Subjects should be debriefed
• Ethical treatment of animals
• Generally research goes before a review board for
approval
Evaluating Research
STRENGTHS AND WEAKNESSES OF
Experiment
Correlation
Surveys
Naturalistic Observation
Case Studies