Thinking Critically With Psychological Science
I. The Need for Psychological Science
a. The limits of Intuition and Common Sense: Many of us believe that our
intuition and common sense are enough to bring forth answers about
human nature. Although intuitions and common sense may aid queries,
they are not free of error.
i. Hindsight Bias : The “I knew-it-all-along” phenomenon.
“Anything seems commonplace, once explained.” Dr. Watson to
Sherlock Holmes.
ii. Judgmental Overconfidence: we tend to think we know more that
we actually do.
Two phenomena – hindsight bias and judgmental overconfidence –
illustrate why we cannot rely solely on intuition and common sense.
iii. Psychological Science
How can we differentiate between uniformed opinions and
examined conclusions?
Science of psychology can help make these examined conclusions,
which lead to our understanding what people feel, think, act, as
they do.
b. The Scientific Attitude: The scientific attitude is composed of curiosity
(passion for exploration), skepticism (doubting and questioning), and
humility (humbleness to accept when wrong).
c.
The Scientific Method: Used by psychologists to construct theories that
organize, summarize, and simplify observations.
.
i. Theory: an explanation that integrates principles, organizes and
predicts behaviors or events. EX. Low self-esteem leads to
depression.
ii. Hypothesis: a testable prediction, often induced by a theory, to
enable us to accept, reject, or revise the theory. EX. People with
low self-esteem are apt to feel more depressed.
iii. Research Observations: would require us to administer tests of
self-esteem and depression to people. Individuals who score low
on self-esteem measures and high on depression test, would
confirm our hypothesis.
II. Description
a. Case Study: a technique in which one person is studied in depth to
reveal underlying behavioral principles.
i. Clinical Study: a form of case study where the therapist
investigates the problems associated with a client.
b. Survey: a technique for ascertaining the self-reported attitudes,
opinions or behaviors of people usually by questioning a representative,
random sample of people .
i. Wording effects: wording can change the results of a survey.
ii. False Consensus Effect: a tendency to overestimate the extent to
which others share our beliefs and behaviors.
iii. Random Sampling: Each member of a population has an equal
chance of inclusion in a sample.
iv. Stratified Sampling: The proportions of individuals in the sample
are the same as in the target population. Ex. If there are 56%
females and 44% males in the target population, in a sample of
100 there should be 56 females and 44 males.
c. Naturalistic Observation: observing and recording behavior of animals
and humans in their natural settings.
Correlation
a measure of the extent to which two factors vary together,
thus how well either factor predicts the other
(Measure of the relationship between 2 variables)
Correlational Coefficient
the mathematical expression of the relationship between
two variables. Ranges from -1 to +1
The closer to (±)1, the stronger the relationship
Ex. -.86 is a stronger relationship than +.44 (.86 is closer
to 1)
Scatterplot
graphed cluster of dots that represent the values of the two
variables. Slope=direction of relationship, scatter=strength
Positive Correlation
two sets of scores tend to rise and fall together. High score
on one measure related to high score on other.
Ex. ACT/SAT score and college GPA
Scatterplot
Negative Correlation
two sets of scores relate inversely. As one value rises, the
other falls. Ex. Tooth brushing and tooth decay
Scatterplot
Correlation and Causation
Correlations help us predict, but we CANNOT determine
cause and effect.
Illusory Correlations
The perception of a relationship where no
relationship exists.
EXPERIMENTS
 Like other sciences, experimentation is the backbone of psychology research.
 Experiments isolate causes and their effects. Only research method that can
determine cause and effect.
 Experiments (1) manipulate factors that interest us, while other factors are kept
under (2) control.
 Most controllable research method.
Independent Variable (IV)
 a factor manipulated by the experimenter. The effect of the independent variable
is the focus of the study.
 For example, when examining the effects of breast feeding upon intelligence,
breast feeding is the independent variable.
More examples of IV:
Dependent Variable
 a factor that may change in response to an independent variable. In psychology, it
is usually a behavior or a mental process.
 For example, in our study on the effect of breast feeding upon intelligence,
intelligence is the dependent variable.
More examples of DV:
Double-Blind Procedures
 In evaluating drug therapies, patients and experimenter’s assistants should remain
unaware of which patients had the real treatment and which patients had the
placebo treatment.
Random Assignment
 Each person has equal chance of being in either the control condition or the
experimental condition
 Assigning participants to experimental (Breast-fed) and control (formula-fed)
conditions by random assignment minimizes pre-existing differences between the
two groups.
 Eliminates bias
Confounding Variables
 Any variable, other than the independent variable, that can influence the
dependent variable.
 EX:
Quasi-Experiment
 Similar to an experiment, but lacking some of the key components, especially
RANDOM ASSIGNMENT
 Sometimes it is not practical, possible, or ethical to randomly assign people to
groups.
 Use pre-existing groups.
Statistical Reasoning
After we gather the data, we must organize, summarize, and make inferences from it to
help us see and interpret what the unaided eye might miss.
Describing Data
We first organize data using graphs.
The following are bar graphs used to represent data.
We must be sure to read the scale labels and note the range so we are not mislead.
Measures of Central Tendency
 Def: a single score that represents a whole set of scores
1. Mode: The most frequently occurring score(s) in a distribution.
2. Mean: The arithmetic average of a distribution. Obtained by adding the scores
and dividing by the total number of scores.
3. Median: The middle score in a distribution; half will fall above it and half are
below it.
Skewed Distribution
A distribution is skewed if one of its tails is longer than the other.
Positively skewed: means that a distribution has a long tail in the positive direction.
Negatively skewed: means that a distribution has a long tail in the negative direction.
*** The Mean can be greatly affected by a few outliers. A couple of really high
scores can make the mean deceptively high, and vice versa.
Measures of Variation
 How diverse or similar scores are
Range: the difference between the highest score and the lowest score in a distribution
Standard Deviation: a computed measure of how much scores vary around the mean
Making Inferences
When can we generalize from the sample?
1. Representative samples are better than biased samples.
2. Less-variable observations are more reliable than those that are more variable.
3. More cases are better than a few.
When is a difference significant?
When the sample averages are reliable and the difference between them is
relatively large. For most psychologists, proof beyond reasonable doubt means not
making much of a finding unless the odds of its occurring by chance are less than 5
percent.
ETHICS
1. Participants must be kept free from harm (physical and psychological).
2. Participants must provide informed consent. They must be informed of the topic
of the experiment, be given the right to chose not to participate, and sign the form.
3. Participants must be allowed to withdraw from the study at any point.
4. Participant’s results must be kept confidential.
5. Participants must be debriefed after the experiments and told of any deception,
the aim, and the findings of the study.